diff --git a/src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.C b/src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.C
index 8aa4168d6d..6558b2543e 100644
--- a/src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.C
+++ b/src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.C
@@ -509,7 +509,7 @@ Foam::autoPtr<Foam::functionObjectList> Foam::functionObjectList::New
 
 Foam::label Foam::functionObjectList::triggerIndex() const
 {
-    return propsDict().getOrDefault<label>("triggerIndex", labelMin);
+    return propsDict().getTrigger();
 }
 
 
diff --git a/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.C b/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.C
index 81a78a1630..3a22981771 100644
--- a/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.C
+++ b/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.C
@@ -79,26 +79,38 @@ Foam::dictionary& Foam::functionObjects::properties::getObjectDict
 }
 
 
-bool Foam::functionObjects::properties::setTrigger
-(
-    const label triggeri
-)
+void Foam::functionObjects::properties::clearTrigger()
 {
-    label oldTriggeri = getOrDefault<label>("triggerIndex", labelMin);
-
-    if (triggeri > oldTriggeri)
-    {
-        set("triggerIndex", triggeri);
-        return true;
-    }
-
-    return false;
+    remove("triggerIndex");
 }
 
 
 Foam::label Foam::functionObjects::properties::getTrigger() const
 {
-    return getOrDefault<label>("triggerIndex", labelMin);
+    // Like getOrDefault, but without reporting missing entry (noisy)
+    label idx = labelMin;
+    readIfPresent("triggerIndex", idx);
+    return idx;
+}
+
+
+bool Foam::functionObjects::properties::setTrigger
+(
+    const label triggeri,
+    bool increaseOnly
+)
+{
+    const label currTriggeri = getTrigger();
+
+    if (increaseOnly ? (triggeri > currTriggeri) : (triggeri != currTriggeri))
+    {
+        set("triggerIndex", triggeri);
+        return true;
+    }
+
+    // TBD: any special handling for triggeri == labelMin - eg, clearTrigger()
+
+    return false;
 }
 
 
diff --git a/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.H b/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.H
index 2e058bfeaf..2860f400ba 100644
--- a/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.H
+++ b/src/OpenFOAM/db/functionObjects/functionObjectProperties/functionObjectProperties.H
@@ -117,11 +117,20 @@ public:
                 const word& entryName
             ) const;
 
+            //- Remove the trigger index from the properties
+            void clearTrigger();
+
             //- Get the current trigger index
             label getTrigger() const;
 
-            //- Set the current trigger index
-            bool setTrigger(const label triggeri);
+            //- Set the trigger index. Normally only if greater than current
+            //
+            //  \param triggeri the new trigger index
+            //  \param increaseOnly (default) only change if new index
+            //      is greater than the current index.
+            //
+            //  \return True if the index changed
+            bool setTrigger(const label triggeri, bool increaseOnly = true);
 
             //- Set dictionary from named object, return true if set
             bool getObjectDict
diff --git a/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.C b/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.C
index 773dbafecf..945445fa87 100644
--- a/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.C
+++ b/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.C
@@ -74,12 +74,9 @@ Foam::dictionary& Foam::functionObjects::stateFunctionObject::propertyDict()
 }
 
 
-bool Foam::functionObjects::stateFunctionObject::setTrigger
-(
-    const label triggeri
-)
+void Foam::functionObjects::stateFunctionObject::clearTrigger()
 {
-    return stateDict().setTrigger(triggeri);
+    return stateDict().clearTrigger();
 }
 
 
@@ -89,6 +86,16 @@ Foam::label Foam::functionObjects::stateFunctionObject::getTrigger() const
 }
 
 
+bool Foam::functionObjects::stateFunctionObject::setTrigger
+(
+    const label triggeri,
+    bool increaseOnly
+)
+{
+    return stateDict().setTrigger(triggeri, increaseOnly);
+}
+
+
 bool Foam::functionObjects::stateFunctionObject::foundProperty
 (
     const word& entryName
diff --git a/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.H b/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.H
index 7dce6ee473..71144f9224 100644
--- a/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.H
+++ b/src/OpenFOAM/db/functionObjects/stateFunctionObject/stateFunctionObject.H
@@ -118,11 +118,20 @@ public:
             //- Return true if the property exists
             bool foundProperty(const word& entryName) const;
 
+            //- Remove the trigger index from the properties
+            void clearTrigger();
+
             //- Get the current trigger index
             label getTrigger() const;
 
-            //- Set the current trigger index
-            bool setTrigger(const label triggeri);
+            //- Set the trigger index. Normally only if greater than current
+            //
+            //  \param triggeri the new trigger index
+            //  \param increaseOnly (default) only change if new index
+            //      is greater than the current index.
+            //
+            //  \return True if the index changed
+            bool setTrigger(const label triggeri, bool increaseOnly = true);
 
             //- Set dictionary, return true if set
             bool getDict
diff --git a/src/OpenFOAM/db/functionObjects/timeControl/timeControlFunctionObject.H b/src/OpenFOAM/db/functionObjects/timeControl/timeControlFunctionObject.H
index 44016ec16b..d12035a586 100644
--- a/src/OpenFOAM/db/functionObjects/timeControl/timeControlFunctionObject.H
+++ b/src/OpenFOAM/db/functionObjects/timeControl/timeControlFunctionObject.H
@@ -80,8 +80,7 @@ class timeControl
 {
 public:
 
-
-    // Public enumerations
+    // Public Enumerations
 
         //- Control mode
         enum class controlMode
@@ -97,7 +96,7 @@ public:
 
 private:
 
-    // Private data
+    // Private Data
 
         //- Input dictionary
         dictionary dict_;
@@ -108,13 +107,13 @@ private:
             //- Control mode (combination of time/trigger behaviour)
             controlMode controlMode_;
 
-            //- Activation time - defaults to -VGREAT
+            //- Activation time - defaults to -VGREAT (ie, active)
             scalar timeStart_;
 
             //- De-activation time - defaults to VGREAT
             scalar timeEnd_;
 
-            //- Activation trigger index - defaults to labelMin
+            //- Activation trigger index - defaults to labelMax (ie, inactive)
             label triggerStart_;
 
             //- De-activation trigger index - defaults to labelMax
diff --git a/src/OpenFOAM/primitives/functions/Function1/Constant/Constant.H b/src/OpenFOAM/primitives/functions/Function1/Constant/Constant.H
index 965bb7d464..e7916f4313 100644
--- a/src/OpenFOAM/primitives/functions/Function1/Constant/Constant.H
+++ b/src/OpenFOAM/primitives/functions/Function1/Constant/Constant.H
@@ -131,6 +131,9 @@ public:
 
     // Member Functions
 
+        //- Change the constant value
+        inline void reset(const Type& val);
+
         //- Return constant value
         virtual inline Type value(const scalar) const;
 
diff --git a/src/OpenFOAM/primitives/functions/Function1/Constant/ConstantI.H b/src/OpenFOAM/primitives/functions/Function1/Constant/ConstantI.H
index 5e05dd30f8..ed120b5d2d 100644
--- a/src/OpenFOAM/primitives/functions/Function1/Constant/ConstantI.H
+++ b/src/OpenFOAM/primitives/functions/Function1/Constant/ConstantI.H
@@ -31,7 +31,14 @@ License
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 template<class Type>
-inline Type Foam::Function1Types::Constant<Type>::value(const scalar x) const
+inline void Foam::Function1Types::Constant<Type>::reset(const Type& val)
+{
+    value_ = val;
+}
+
+
+template<class Type>
+inline Type Foam::Function1Types::Constant<Type>::value(const scalar) const
 {
     return value_;
 }
diff --git a/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.C b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.C
new file mode 100644
index 0000000000..cc94b94eb5
--- /dev/null
+++ b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.C
@@ -0,0 +1,106 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "FunctionObjectTrigger.H"
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+template<class Type>
+void Foam::Function1Types::FunctionObjectTrigger<Type>::read
+(
+    const dictionary& coeffs
+)
+{
+    triggers_ = coeffs.get<labelList>("triggers", keyType::LITERAL);
+    defaultValue_ =
+        coeffs.getOrDefault("defaultValue", false, keyType::LITERAL);
+}
+
+
+template<class Type>
+Foam::Function1Types::FunctionObjectTrigger<Type>::FunctionObjectTrigger
+(
+    const word& entryName,
+    const dictionary& dict,
+    const objectRegistry* obrPtr
+)
+:
+    Function1<Type>(entryName, dict, obrPtr),
+    triggers_(),
+    defaultValue_(false)
+{
+    read(dict);
+}
+
+
+template<class Type>
+Foam::Function1Types::FunctionObjectTrigger<Type>::FunctionObjectTrigger
+(
+    const FunctionObjectTrigger<Type>& rhs
+)
+:
+    Function1<Type>(rhs),
+    triggers_(rhs.triggers_),
+    defaultValue_(rhs.defaultValue_)
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class Type>
+void Foam::Function1Types::FunctionObjectTrigger<Type>::writeEntries
+(
+    Ostream& os
+) const
+{
+    os.writeKeyword("triggers");
+    flatOutput(triggers_);
+    os.endEntry();
+
+    if (defaultValue_)
+    {
+        os.writeEntry("default", "true");
+    }
+}
+
+
+template<class Type>
+void Foam::Function1Types::FunctionObjectTrigger<Type>::writeData
+(
+    Ostream& os
+) const
+{
+    Function1<Type>::writeData(os);
+    os.endEntry();
+
+    os.beginBlock(word(this->name() + "Coeffs"));
+    writeEntries(os);
+    os.endBlock();
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.H b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.H
new file mode 100644
index 0000000000..a534c8153e
--- /dev/null
+++ b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTrigger.H
@@ -0,0 +1,178 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::Function1Types::FunctionObjectTrigger
+
+Description
+    Returns a 0/1 value corresponding to function object trigger levels.
+
+    Usage:
+    \verbatim
+        <entryName> functionObjectTrigger;
+        <entryName>Coeffs
+        {
+            triggers        (1 3 5);
+            defaultValue    false;  // Optional
+        }
+    \endverbatim
+
+    Where:
+    \table
+        Property | Description                                  | Required
+        triggers | List of active trigger states to check for   | yes |
+        defaultValue | Treatment for unactivated trigger state  | no  | false
+    \endtable
+
+    In some circumstances, it can be useful to treat an unactivated trigger
+    as being true. This is the role of the "defaultValue" keyword.
+
+Note
+- does not implement integrate()
+
+SourceFiles
+    FunctionObjectTrigger.C
+    FunctionObjectTriggerI.H
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef Function1Types_FunctionObjectTrigger_H
+#define Function1Types_FunctionObjectTrigger_H
+
+#include "Function1.H"
+#include "labelList.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace Function1Types
+{
+
+/*---------------------------------------------------------------------------*\
+                     Class FunctionObjectTrigger Declaration
+\*---------------------------------------------------------------------------*/
+
+template<class Type>
+class FunctionObjectTrigger
+:
+    public Function1<Type>
+{
+
+    // Private Data
+
+        //- Trigger indices when it is considered active
+        labelList triggers_;
+
+        //- Treatment for unactivated trigger state (true/false)
+        bool defaultValue_;
+
+
+    // Private Member Functions
+
+        //- Is the trigger considered active?
+        inline bool active() const;
+
+        //- Read the coefficients from the given dictionary
+        void read(const dictionary& coeffs);
+
+
+public:
+
+    //- Runtime type information
+    TypeName("functionObjectTrigger");
+
+
+    // Generated Methods
+
+        //- No copy assignment
+        void operator=(const FunctionObjectTrigger<Type>&) = delete;
+
+
+    // Constructors
+
+        //- Construct from entry name, dictionary and optional registry
+        FunctionObjectTrigger
+        (
+            const word& entryName,
+            const dictionary& dict,
+            const objectRegistry* obrPtr = nullptr
+        );
+
+        //- Copy construct
+        explicit FunctionObjectTrigger(const FunctionObjectTrigger<Type>& rhs);
+
+        //- Construct and return a clone
+        virtual tmp<Function1<Type>> clone() const
+        {
+            return tmp<Function1<Type>>(new FunctionObjectTrigger<Type>(*this));
+        }
+
+
+    //- Destructor
+    virtual ~FunctionObjectTrigger() = default;
+
+
+    // Member Functions
+
+        //- Return the trigger indices
+        inline const labelList& triggers() const noexcept;
+
+        //- Change the trigger indices
+        inline void resetTriggers(const labelUList& indices);
+
+
+        //- Return 0/1 value at current time
+        virtual inline Type value(const scalar /*unused*/) const;
+
+        //- Integrate between two (scalar) values. Not implemented!
+        virtual inline Type integrate(const scalar, const scalar) const;
+
+        //- Write in dictionary format
+        virtual void writeData(Ostream& os) const;
+
+        //- Write coefficient entries in dictionary format
+        void writeEntries(Ostream& os) const;
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Function1Types
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#include "FunctionObjectTriggerI.H"
+
+#ifdef NoRepository
+    #include "FunctionObjectTrigger.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTriggerI.H b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTriggerI.H
new file mode 100644
index 0000000000..83208c63b4
--- /dev/null
+++ b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectTrigger/FunctionObjectTriggerI.H
@@ -0,0 +1,89 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "FunctionObjectTrigger.H"
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class Type>
+inline bool Foam::Function1Types::FunctionObjectTrigger<Type>::active() const
+{
+    if (triggers_.empty())
+    {
+        return false;
+    }
+
+    const label idx = this->time().functionObjects().triggerIndex();
+
+    return
+    (
+        idx == labelMin ? defaultValue_ : triggers_.found(idx)
+    );
+}
+
+
+template<class Type>
+inline const Foam::labelList&
+Foam::Function1Types::FunctionObjectTrigger<Type>::triggers() const noexcept
+{
+    return triggers_;
+}
+
+
+template<class Type>
+inline void Foam::Function1Types::FunctionObjectTrigger<Type>::resetTriggers
+(
+    const labelUList& indices
+)
+{
+    triggers_ = indices;
+}
+
+
+template<class Type>
+inline Type Foam::Function1Types::FunctionObjectTrigger<Type>::value
+(
+    const scalar /*unused*/
+) const
+{
+    return this->active() ? pTraits<Type>::one : pTraits<Type>::zero;
+}
+
+
+template<class Type>
+inline Type Foam::Function1Types::FunctionObjectTrigger<Type>::integrate
+(
+    const scalar x1,
+    const scalar x2
+) const
+{
+    NotImplemented;
+    return pTraits<Type>::zero;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/functions/Function1/FunctionObjectValue/FunctionObjectValue.H b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectValue/FunctionObjectValue.H
index 501b2b1a72..103965f937 100644
--- a/src/OpenFOAM/primitives/functions/Function1/FunctionObjectValue/FunctionObjectValue.H
+++ b/src/OpenFOAM/primitives/functions/Function1/FunctionObjectValue/FunctionObjectValue.H
@@ -40,12 +40,12 @@ Description
         }
     \endverbatim
 
-
 Note
 - does not implement integrate()
 
 SourceFiles
     FunctionObjectValue.C
+    FunctionObjectValueI.H
 
 \*---------------------------------------------------------------------------*/
 
@@ -129,10 +129,10 @@ public:
 
     // Member Functions
 
-        //- Return value for time t
-        virtual inline Type value(const scalar t) const;
+        //- Return value at current time
+        virtual inline Type value(const scalar /*unused*/) const;
 
-        //- Integrate between two (scalar) values
+        //- Integrate between two (scalar) values. Not implemented!
         virtual Type integrate(const scalar x1, const scalar x2) const;
 
         //- Write in dictionary format
diff --git a/src/OpenFOAM/primitives/functions/Function1/makeFunction1s.C b/src/OpenFOAM/primitives/functions/Function1/makeFunction1s.C
index 179209c655..03279221ad 100644
--- a/src/OpenFOAM/primitives/functions/Function1/makeFunction1s.C
+++ b/src/OpenFOAM/primitives/functions/Function1/makeFunction1s.C
@@ -39,6 +39,7 @@ License
 #include "TableFile.H"
 #include "Scale.H"
 #include "InputValueMapper.H"
+#include "FunctionObjectTrigger.H"
 #include "FunctionObjectValue.H"
 #include "fieldTypes.H"
 
@@ -73,6 +74,10 @@ namespace Foam
     makeFunction1(label);
     makeFunction1Type(Constant, label);
 
+    makeFunction1Type(FunctionObjectTrigger, label);
+    makeFunction1Type(FunctionObjectTrigger, scalar);
+    // Only (label/scalar) makes sense for triggers
+
     makeFunction1s(scalar);
     makeFunction1s(vector);
     makeFunction1s(sphericalTensor);