If That Then This (IfTTT) is a web service that lets you link two or more smart systems. IfTTT applets use a trigger action from one system to invoke actions in other systems – for example, you could use an ‘everyone’s gone out’ trigger from your heating system to enact a ‘turn everything off’ command for your lights.
You can create three IfTTT applets for free, but for complex projects you may need the new IfTTT Pro subscription.