Windows are an existing opening, and may also be exploited by a burglar if not adequately secured. Since the sound of breaking glass carries further than almost any other noise, and elicits a response from most people who hear it, burglars are extremely reluctant to break it. Therefore, if you protect your windows, they won't be a security liability, and can provide some security benefit.

The best single protection for windows is storm glazing. Installation of auxiliary storm windows on an existing house puts a whole additional security layer in place, and usually provides very adequate security. On new homes, double and triple glazing is normaly used for insulatiohn value, and accomplishes the same function of defense against simple breakage. Multiple layers of glazing are desirable.

Windows should be equipped with a locking device. Most manufacturers install devices which provide very adequate security, if properly used and maintained. In order to ensure that a window could be used for emergency exit, any lock used on windows should operate from the inside.

Older homes may need supplemental security devices if the original locks are no longer operable or if none exist. Double-hung sash windows can be secured with a pin-lock similar to those described for sliding doors. To secure the inside and outside sashes, a hole is drilled completely through the inside sash so that a pin can be inserted which projects into the outside sash. This will secure both in place. Care must be taken not to drill too closely to the glazing.

Consider installing "stops" on windows to prevent them from being opened more than a pre-selected height, typically 6 or 8 inches, which is adequate for ventilation, but won't admit a human body. This is readily accomplished by screwing a block of wood (or metal to match the window, if available) into the track above the sliding sash. With stops in place, even if a would-be intruder defeats your lock, he cannot open the sash more than the limited width without breaking glass. Thumbscrew metal stops are also available for some windows, which are easier to adjust/remove than traditional wooden stops. Obviously, "stops" also limit the ability for you to use the windows as a means of emergency exit, requiring you to break out the window to quickly exit a room.

Security grilles or bars are not recommended for home use. They're vulnerable to manipulation from the outside because they must be equipped with a device to enable them to be opened in the event of an emergency. While they give the appearance of being secure, any competent burglar knows they really aren't very effective.