Windows are burglars second choice. Alarms trumpet the arrival of an intruder. If possible, invest in an alarm with a motion detector. Have a phone in each room so that help is always within reach. Keep shrubbery trimmed so as not to provide a cover for a burglar.
Dogs are great alarms, and most criminals won t risk a confrontation with a dog of any size.
Verbally answering through the closed door lets them know that the apartment is not empty. If the stranger is wearing a uniform, make them show you identification. If in doubt, have them wait outside while you call their company for verification. If a stranger asks to use you phone, ask for the number and make the call while they wait outside. Furthermore, if some one dials your number by mistake, do not reveal your phone number, simply advise them to try their number again.