For door locks, use a solid, commercial deadbolt. Fit the door with a two-lock sequence, each lock being opened with a different key. Electronic alarms can add greatly to the security of your building, but you must back up the system with patrol officers. Depending on the area you want to protect, you can choose models activated by pressure sensors, heat sensors, motion detectors, or photoelectric cells. Police departments rightly complain about false alarms, but they are usually caused by the person who sets the system, not the system itself.
Advertising pays, even in security.
Display well-worded, highly visible signs warning that the facility is patrolled and outfitted with alarm systems. Not all intruders will be scared off, but many will. Electric fences, booby traps, and such devices are not particularly advisable in this day of deep-pocket suits and generous juries. Other means of access. Cover utility openings such as air-conditioner ducts, skylights, and sewer drains with bars or screens.