it may be a more universal solution for the node/switch to use the request(uint8_t childSensorId, uint8_t variableType) function and resend the command to the node/relayActuator after a timeout. This is what @jkandasa mentioned in his post earlier. Still if the node/switch receives the request() it does not know what sensor sent it. If this was contained in the message variable we could implement a fairly robust solution to this.