I've learned that guys that want to be in chastity and serve that way can be trusted not to do anything unauthorised and that is really the only kind of sub I am interested in doing keyholding with. However, I think it is psychologically powerful to have them not in control of the key. For the last few years I have been using the clear electric kitchen safes. They have to put the keys in and set the timer to what I say. In an absolute emergency they could smash the box if necessary, but in the meantime the keys are safely locked away.

There are some new devices that have come on the market within the last year that hold the keys and can be locked/unlocked with an app. I haven't found one that is affordable and fits all my needs yet but I think it's coming eventually.