Leaving a way back in after you crack a lock is prudent- and tradition. Keeping physical keys worked well in the past- bump key encpryptions are similar but things like this? Make a job so much easier if you know you'll be working the same building more than once. You set it up when you do recon, then when the actual job comes? You save that much more time and pain.

[ He does the same check for the alarm and security system, and it's still handled. Good. ]

The basic encryption I learned when I was a lad. The rest- came from an old partner.