[Mister_Snuggles]

> The solution I've come up with but haven't yet put into action is to use an ESP device, with some sort of contact switch which sits _in_ the hole where the lock goes and detects whether the lock (bolt?) is physically present.

Another option is to disassemble a door/window sensor and replace its reed switch with a contact switch, much like you want to do with the ESP.

[alias_neo]

Heh, I don't know how that didn't occur to me. I guess I'm susceptible to overcomplicating things by trying to build it rather than just use something that's already 90% there.

I'll have to give this a try now you've suggested it, I've got a few spare Zigbee doors sensors, Ring and IKEA so will be interesting to see which is better suited.

Thanks for the suggestion!