Comment by neilv

One rental apartment where I'd changed the lock core, one day the nice handyman admired the fancy Mul-T-Lock style key while I was letting him in, and later remarked about it to landlord.

So I had to put the old cylinder back in, because of condo rules about the property management company needing keys.

(Though I later learned that the property management company might not have been able to find my unit's key if they ever wanted to. One day, the fire department was at the building, trying to get into a different unit, which had an alarm sounding, but they found that the key box was empty. I was there, so I called the management company, but they refused to send a runner with the key. Even after I handed my phone to the firefighter in charge, and he identified himself and asked them again. :)