Bollo's Magic Button

a button forms on an open-able object's lock, things ranging from book to gate, preventing them from being opened or dispelled, unless it is a area of effect dispel, from the other side. any person can unbutton or button up the object to deactivate or reactivate the effect. does not make the door stronger. if the door is locked, the person must unbutton the object to insert the key. if someone tries to use a key from the outside while the button is on, it won't turn.

 Knock still works though, it is as if the button unbuttons itself.

Bollo- And they said buttons couldn't stop them. 

from Bollo's bag of tricks