Management posted a memo on notice boards about a few suspicious looking persons seen loitering at blocks A and C recently. I asked around and some residents confirmed that these scoundrels are probably also responsible for 'fixing' the lobby locking mechanism so that it could not lock. Not too difficult as they would just need to prevent the circuit from connecting by sticking a piece of paper, etc onto the metal/magnetic section on the door.
Anyway a unit (or more) has been broken into recently. Do be alert and notify the guards if you see anything suspicious.