There was also an old version of the Lockitron. My understanding is that the old one was a deadbolt replacement while the new one goes over an existing deadbolt

There was also an old version of the Lockitron. My understanding is that the old one was a deadbolt replacement while the new one goes over an existing deadbolt lock. They still sell the Lockitron Access (https://lockitron.com/store/buzzer https://lockitron.com/store/buzzer) which works with electronic locks. It is possible that he has one of those.