At my house, it's a Yale lock which as Tara has mentioned, they lock automatically because essentially they're a latch with a key. Ironically it's a valid term to say "The door is on the latch" when you engage a small locking mechanism what prevents the tumbler from being turned with the "latch" component retracted so the front door stays open.

At my mom's it's one of those upvc doors that double glazing firms install. It has like 6 locks built in to it which engage on a lift of the door handle and locks with a key both inside and out. However when people are awake and in the house (during the day for example) the door is often unlocked.