I want to make a rule to know when I've brought the trash can back to it's location.
There is at least 100 feet between it's normal location and where it is for trash pickup day.
So I'm wondering if there is any way to trigger on the device returning to the network. Or if I can trigger on signal strength or which device is used as a repeater?
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I am not aware of any way to do what you are requesting. I don't think Zwave works that way with knowing what device is attached to which repeater, at least not in a way we can utilize for automations. A sensor that you would use for this probably isn't a geolocation device. And most of the time if you start messing with the Zwave mesh by adding and removing devices, you probably will make the Zwave mesh unstable.
Unfortunately there are almost no choice for presence fobs in Zwave. Is there a way you could use a contact sensor on the house and mount a strong magnet to the trash can? Or use some type of pressure mat that it could sit on? Maybe some other way to detect if the can is physically sitting in the right spot?