What can I get for my grandma so she doesn't forget her keys again?

[AintNobodyHereButUsChickens]

She sometimes leaves her keys in her front door, and her front door is on the street so any passerby could take her keys and help themselves to the contents of her house. I'd like to get some sort of alarm that goes off when she gets a certain distance from the keys. My mum used to have something like this many, many, many years ago and she doesn't remember what it was called or where it was from. Ideally one part would attach to her keys and the other part would go in her handbag or pocket.

Can anyone help?

I have a plastic spiral keychain thing that attaches my doorkey to my handbag, so I don't actually take the key out of the bag to open it.

MIL does the same. She leaves a key on the inside of her door so that she can lock it inside (her big lock opens from the outside even with a key in the lock on the inside). Hers was more to stop her locking herself out of her yale lock though.