Turn on smart switch based on action of another "dumb" circuit


Hi, I may be overlooking something really simple here, but Im trying to figure out how I may go about switching on and off one (or more) Zwave light switches based on the status of an existing but dumb lighting circuit.

Due to a bit of an oversight when having the house extended and rewired, I now wish to add some more outside lights on the house, I would like them to come on at the same time as the existing exterior decorative lights which are controlled via a dusk to dawn sensor.

There is no way to extend the existing circuit without major upheaval now.

So, how would I go about switching on or off a zwave switch based on the status of another dumb circuit? Is this possible?

(Colin Weir) #2

Can the existing light take a new smart bulb? Is it not possible to put a smart switch on the one remaining light?


You have two options here: either event monitoring or current monitoring.

For event monitoring, life is simple. You just put a lux sensor near the dumb lights and then when it comes on between sunset and sunrise you know those lights came on, and you trigger the smart lights off of that. No wiring required. There may be a slight lag in order to process everything, but for this kind of use case It’s usually acceptable. So first the dumb lights come on and then A few seconds later the smart lights come on. This option can work even if the dumb lights are battery powered.

Alternatively, you need to wire something into the circuit that can detect the change in draw. And that something needs to be able to communicate with SmartThings.

The Fortrezz Mimolite is a popular device for this purpose and is sold in both the US and UK frequencies. It works well with SmartThings. It’s just that it’s a bit expensive. People do use them to monitor all kinds of non-network devices, and it has a number of advanced features including being able to set a range of draw to monitor.


There should be some less expensive options but I’m not as familiar with the UK devices. The Fibaro door sensor does have dry contacts and might be usable (so that it would report open when the nonnetworked lights were on and closed when the nonnetworked lights are off, for example), but I honestly don’t know if it would work without requiring a transformer.

Hopefully someone who has more experience with UK devices can comment further on the options.

(Robin) #4

The Fibaro door / window sensor wire terminals can only take a dry contact i.e. a non powered switch / button / magnetic reed contact. You would need a relay to seperate the mains voltage from the Fibaro or it will go pop, and for the cost savings you’ll be loosing a lot of functionality.

As asked further up, why not just make the ‘dumb’ D2D circuit smart? It must have a switch somewhere in addition to the D2D? Or at least have an accessible feed spured off somewhere?

If you can’t access the power feed at source, put a device in the primary light fitting itself (the one at the start of the circuit)… the Fibaro switch or dimmer modules for example can go in the primary fitting quite happily as can, I think, many other micro modules.

Bypass / remove the D2D, fit a smart switch / module and setup your new and old circuits to toggle programmatically based on sunset / sunrise rules (and more).