I think the reliability problem was a result if the safe door being insulated would muffle the knock and the lock wouldn't operate since it misinterpreted the knock. An Isreali product that is still sold today but for door lock applications and typically the lock is installed on the jamb. Look for Knock-n-Lock or PulseCode.
BBE.

Quote Originally Posted by Tom Gordon View Post
I thought that it would be a great way to retrofit a more secure type of locking on antique safes, that is practical to use and entirely hidden - shame about it's reliability.