That sounds like it could develop into unhealthy behavior. Glad it works for you though. Personally I do the 3 pocket pat down every time. Left, right, back. Keys, phone, wallet. If either pocket is empty then something is seriously wrong.
Sometimes I'll do this while I'm using my phone, and momentarily freak out because my phone pocket is empty.
* The ignition (my car plays a chime if I open the door with the keys still in the ignition) * My pocket (self explanatory) * My lap (they will fall and make a racket if I stand up without grabbing them first)
My father's system: Only lock doors from the outside, using a key. It's hard to lock yourself out that way. (Not helpful if you live in an apartment with doors that lock automatically.)