Lost Item Prevention Phone Number Tag Keychain. I attach these phone number tags to all my keys: house keys, bicycle keys, and car keys. I find them very useful because if I drop my keys somewhere, the person who finds them can call me. This is an essential item, especially for keys that children carry. One phone number tag is included with each keychain, but additional phone number tags can be added for 300 yen each. If you would like to add more, please comment. I will adjust the price.