diff --git a/src/property.ts b/src/property.ts
index af448bf..89b75d0 100644
--- a/src/property.ts
+++ b/src/property.ts
@@ -118,7 +118,7 @@ class Property<ValueType = AnyType> {
    *
    * @returns {*} The current value
    */
-  getValue(): ValueType {
+  getValue(): Promise<ValueType> {
     return this.value.get();
   }
 
@@ -127,9 +127,9 @@ class Property<ValueType = AnyType> {
    *
    * @param {*} value The value to set
    */
-  setValue(value: ValueType): void {
+  setValue(value: ValueType): Promise<void> {
     this.validateValue(value);
-    this.value.set(value);
+    return this.value.set(value);
   }
 
   /**
diff --git a/src/server.ts b/src/server.ts
index 7de2139..d2ddbd4 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -225,7 +225,7 @@ class ThingHandler extends BaseHandler {
         data: Record<string, unknown>;
       };
       try {
-        message = JSON.parse(msg as string);
+        message = JSON.parse((msg as unknown) as string);
       } catch (e1) {
         try {
           ws.send(
@@ -274,7 +274,7 @@ class ThingHandler extends BaseHandler {
                   messageType: 'error',
                   data: {
                     status: '400 Bad Request',
-                    message: e.message,
+                    message: e instanceof Error ? e.message : 'unknown reason',
                   },
                 })
               );
@@ -378,7 +378,14 @@ class PropertyHandler extends BaseHandler {
 
     const propertyName = req.params.propertyName;
     if (thing.hasProperty(propertyName)) {
-      res.json({ [propertyName]: thing.getProperty(propertyName) });
+      thing
+        .getProperty(propertyName)
+        .then((value) => {
+          res.json({ [propertyName]: value });
+        })
+        .catch((e) => {
+          res.status(500).end(e.toString());
+        });
     } else {
       res.status(404).end();
     }
@@ -399,19 +406,18 @@ class PropertyHandler extends BaseHandler {
 
     const propertyName = req.params.propertyName;
     if (!req.body.hasOwnProperty(propertyName)) {
-      res.status(400).end();
+      res.status(404).end();
       return;
     }
 
     if (thing.hasProperty(propertyName)) {
-      try {
-        thing.setProperty(propertyName, req.body[propertyName]);
-      } catch (e) {
-        res.status(400).end();
-        return;
-      }
-
-      res.json({ [propertyName]: thing.getProperty(propertyName) });
+      thing
+        .setProperty(propertyName, req.body[propertyName])
+        .then(() => thing.getProperty(propertyName))
+        .then((value) => res.json({ [propertyName]: value }))
+        .catch((e) => {
+          res.status(500).end(e.toString());
+        });
     } else {
       res.status(404).end();
     }
diff --git a/src/thing.ts b/src/thing.ts
index 34dad27..831a5a1 100644
--- a/src/thing.ts
+++ b/src/thing.ts
@@ -337,13 +337,13 @@ class Thing {
    *
    * @returns {*} Current property value if found, else null
    */
-  getProperty(propertyName: string): unknown | null {
+  getProperty(propertyName: string): Promise<unknown | null> {
     const prop = this.findProperty(propertyName);
     if (prop) {
       return prop.getValue();
     }
 
-    return null;
+    return Promise.reject();
   }
 
   /**
@@ -351,13 +351,18 @@ class Thing {
    *
    * Returns an object of propertyName -> value.
    */
-  getProperties(): Record<string, unknown> {
+  getProperties(): Promise<Record<string, unknown>> {
     const props: Record<string, unknown> = {};
+    const promises: Promise<void>[] = [];
     for (const name in this.properties) {
-      props[name] = this.properties[name].getValue();
+      promises.push(
+        this.properties[name].getValue().then((value) => {
+          props[name] = value;
+        })
+      );
     }
 
-    return props;
+    return Promise.all(promises).then(() => props);
   }
 
   /**
@@ -377,13 +382,13 @@ class Thing {
    * @param {String} propertyName Name of the property to set
    * @param {*} value Value to set
    */
-  setProperty(propertyName: string, value: AnyType): void {
+  setProperty(propertyName: string, value: AnyType): Promise<void> {
     const prop = this.findProperty(propertyName);
     if (!prop) {
-      return;
+      return Promise.reject();
     }
 
-    prop.setValue(value);
+    return prop.setValue(value);
   }
 
   /**
@@ -586,20 +591,22 @@ class Thing {
    * @param {Object} property The property that changed
    */
   propertyNotify(property: Property<AnyType>): void {
-    const message = JSON.stringify({
-      messageType: 'propertyStatus',
-      data: {
-        [property.getName()]: property.getValue(),
-      },
-    });
+    property.getValue().then((value) => {
+      const message = JSON.stringify({
+        messageType: 'propertyStatus',
+        data: {
+          [property.getName()]: value,
+        },
+      });
 
-    for (const subscriber of this.subscribers) {
-      try {
-        subscriber.send(message);
-      } catch (e) {
-        // do nothing
+      for (const subscriber of this.subscribers) {
+        try {
+          subscriber.send(message);
+        } catch (e) {
+          // do nothing
+        }
       }
-    }
+    });
   }
 
   /**
diff --git a/src/value.ts b/src/value.ts
index a0ba095..70c7b8b 100644
--- a/src/value.ts
+++ b/src/value.ts
@@ -20,6 +20,8 @@ class Value<ValueType = AnyType> extends EventEmitter {
 
   private valueForwarder: Value.Forwarder<ValueType> | null;
 
+  private valueRequestor: Value.Requestor<ValueType> | null;
+
   /**
    * Initialize the object.
    *
@@ -27,10 +29,15 @@ class Value<ValueType = AnyType> extends EventEmitter {
    * @param {function?} valueForwarder The method that updates the actual value
    *                                   on the thing
    */
-  constructor(initialValue: ValueType, valueForwarder: Value.Forwarder<ValueType> | null = null) {
+  constructor(
+    initialValue: ValueType,
+    valueForwarder: Value.Forwarder<ValueType> | null = null,
+    valueRequestor: Value.Requestor<ValueType> | null = null
+  ) {
     super();
     this.lastValue = initialValue;
     this.valueForwarder = valueForwarder;
+    this.valueRequestor = valueRequestor;
   }
 
   /**
@@ -38,12 +45,10 @@ class Value<ValueType = AnyType> extends EventEmitter {
    *
    * @param {*} value Value to set
    */
-  set(value: ValueType): void {
-    if (this.valueForwarder) {
-      this.valueForwarder(value);
-    }
-
-    this.notifyOfExternalUpdate(value);
+  set(value: ValueType): Promise<void> {
+    return Promise.resolve(this.valueForwarder ? this.valueForwarder(value) : undefined).then(() =>
+      this.notifyOfExternalUpdate(value)
+    );
   }
 
   /**
@@ -51,8 +56,14 @@ class Value<ValueType = AnyType> extends EventEmitter {
    *
    * @returns the value.
    */
-  get(): ValueType {
-    return this.lastValue;
+  get(): Promise<ValueType> {
+    if (this.valueRequestor) {
+      return Promise.resolve(this.valueRequestor()).then((newValue) => {
+        this.notifyOfExternalUpdate(newValue);
+        return newValue;
+      });
+    }
+    return Promise.resolve(this.lastValue);
   }
 
   /**
@@ -69,7 +80,8 @@ class Value<ValueType = AnyType> extends EventEmitter {
 }
 
 declare namespace Value {
-  export type Forwarder<T> = (value: T) => void;
+  export type Forwarder<T> = (value: T) => void | Promise<void>;
+  export type Requestor<T> = () => T | Promise<T>;
 }
 
 export = Value;