As explained in section 12.0 of the manual.  The “LOCK” feature is turned "OFF" as a factory default setting. 

If your T-Lock's LCD displays "LOCK", then lift-off handset and input *123456# (star key, then 1 2 3 4 5 6 then the pound key) to unlock (e.g. turn "OFF" the lock function), and enable all T-Lock's functions.  Note: Make  sure you have a working handset connected to the PHONE socket on the Call Blocker.

To Lock it, you may lift-off handset and input *000111# to turn "ON" the LOCK feature and LOCK all functions (LCD displays "LOCK"). 

If you continue with issues, please contact us.