That sucks to have someone get in your flat.
The locks and doors on modern flats here in CZ are insane, on my flat I have a steel armoured door and the lock puts around ten 1cm diameter bolts into the door frame (also armoured and set into the masonary) around the top and 2 sides. The key is a double bit one and the bolts are geared so you have to turn the key about 3 times to wind the bolts in our out. It's surprising how little protection in the form of locks we use in the UK, usually a yale but maybe a 5 lever mortice too if you're lucky.