For a few years we owned two houses, a boat and a Motorhome. In order to simplify, I changed the lockset on one house to be the same brand as the other, then had the keys made the same. When we bought the Motorhome, it came with that same brand of deadbolt on the door, so I had the key made the same. The boat, much more difficult, so it remains unlike anything else and seldom gets locked. The first house is gone, the Motorhome is gone, so we are now down to the usual complication of having everything on different keys.