Mini – don’t loose me ringing device

This idea is for a small ringing device that can be added to eg. your bunch of keys. It would just contain a sim card and very minimal electronics to function. You can then ring the device to find your bunch of keys. It might be keyring specific at first and be about the size of a usb pen but this could be evolved to become much smaller over time. I’m always misplacing my keys and thinking, at least if it was my phone i can ring it!