We recommend you to use your own phone no. with a different billing address than where the security item belongs.
You may use e-mail forwarding. This means you register an e-mail address that my be totally anonymous, like firstname.lastname@example.org
Use your anonymous e-mail address when registering as an owner with the Register Owner for your safety items. This e-mail forwarding service will forward your e-mails to your original and preferred e-mail address.
You may use your post box address if it’s not in the same building.
If you have connections to any address not related to the keys or safety item, you may use that address.
For private keys, your work address may be a good choice.
You may give an anonymous name to your profile as not to be looked up in any social media. Your name may be like
First name: Anonymous
Family name: Keyholder.