How to avoid stranger broke into the home?

When the child is alone at home, avoid stranger enters and the risk of unexpected.
Alone at home, to lock doors, security door, guards against the fence.
If someone knock at, do not blindly open the door, first observation or isolation of the out come from the door mirror of identity, if strangers, should not open the door.
If someone to salesmen, mechanics and other identity requirements open the door, may account for the House does not need these services, please leave; if someone from parents \' colleagues, friends or distant relatives of identity requires to open the door, nor believe, can ask their parents back home again. Strangers refused to leave, insisting on human indoor, can claim to be telephoned the police station, or call out to the balcony, window, loudly, to the neighbors, pedestrians to beg, to deter forced its departure.
Not to invite the people who are not familiar with the guest in the home, against the bad guys exploit.