You can't. You don't have a passkey until you try to pair with a device. If someone tries to pair with your N810, it should ask you if you want to permit it, and ask you for a key. All you need to do is say no.

One more time, your N810 has no passkey. You give it a unique key each time you want to pair with another device. Whoever you're accessing has their phone set up to accept anything, which isn't a good idea.