Many can be opened with a default admin password:

Here’s a fun little tip: You can open most Sentex key pad-access doors by typing in the following code:

***00000099#*

The first *** are to enter into the admin mode, 000000 (six zeroes) is the factory-default password, 99# opens the door, and * exits the admin mode (make sure you press this or the access box will be left in admin mode!)