Be sure your outside doors have deadbolt locks. Grills over the windows are useless unless they are actually set into the concrete around the window, rather than screwed or plastered into place. Give them a strong tug to check; they shouldn't move. Change locks when you move into a house and keep close control over who gets copies of keys. Sliding glass doors can be secured by either drilling holes through the frames and inserting a nail, or placing something like a broomstick in the track behind the door.
Lock fuse boxes and electrical panels.
Solid wooden front doors, peepholes, and intercoms are suggested for further security. Never leave keys in locks, especially near windows.
It is also suggested that you use caution regarding what your staff knows about your safety precautions—for example, where your safe is and where money and valuables are kept. It is important to be careful as to who is allowed inside your house; casual visitors with your staff and door-to-door vendors may use the opportunity to "case the joint." Also, many break-ins occur after workmen have been in your house.