Samsung SmartThings Presence Sensor

You can find lost keys

Not loud enough

Useless

Does what is says on the tin

A bit expensive

So easy to understand.

Easy setup and links well to most IoT in the house

Only links to one Philips Hue hub so only half the house lights are connected. Also does not link to Nest without a lot of messing about. Need to be a bit of a techie to use beyond the basics. Also does not work with HomeKit (SIRI)

To plasticy for a key tag

Its good when it works.

Very unreliable.

It works and is of a reasonable size. Built in alarm could be handy if you are the type to lose your keys or remote control if you can attach it to that somehow.

A phone has the same functionality and works as the same trigger, so this is only really useful for a family member without a smart phone (who lets be honest will probably object to carrying this around!) or a pet like a cat.