All modern deadbolt have a similar operation as far as the latch goes. There in this sort of arm inside that must completely straight for the bolt to not easily be pushed back, like your elbow. The most important thing is that the bolt is FULLY EXTENDED, otherwise someone could use a butter knife to work the bolt back into the unlocked position. When the bolt is fully extended, you could hit the end of the bolt with a hammer and it won't budge.

So what I often run into while working on people's locks is the hole that the deadbolt latch goes into isn't deep enough for the bolt to be fully extended. This is a big problem that's very easy to fix, and until you do, your door is not truly locked.