The LULU Real Key is a real prim-based key that will only work when sub is nearby. Only the sub’s owner can get and use the key. If you’re the sub and are un-owned, you can temporarily set yourself as owner (Click the white LULU logo on the HUD. HUD Menu > owner… > add… > self).
If you haven’t already done so, you can get the keys from the LULU Key Box.
To use the key, simply wear it when your sub is nearby and she is wearing the appropriate LULU gear (otherwise there is nothing to lock or unlock!). Also, you must be a current owner of your sub to use the key. You need to be close to, and facing your sub, before you can lock and unlock. You can use the key to order her over. After use, you can send sub back. Your key will automatically detach back to inventory.
Using the key saves the time (in SL time) when the sub was last locked, and by whom. So, if the timestamp doesn’t match, it means your sub has been naughty and found a way to cheat. Interrogate her (even if you have to whip it out of her!) and IM Lulu with her secret. Or send her to Lulu for interrogation :P