Common sense should tell you that multiple locks and standard door alarms will only go so far in terms of protecting your house -- that is, as long as you have windows. Even a rank amateur thief can toss a rock through a pane of glass and gain gleeful entry. That's why the home security industry came up with a glass break sensor, a product that has been evolving ever since.
At first, the glass break sensor consisted of a series of foil strips that had to be affixed to every glass pane. One advantage was that their ugliness made them obvious to potential intruders. A disadvantage was that their ugliness made them obvious to everyone else.
The first foil strips worked on the premise that breaking the window would inevitably tear the glass break sensor, which would sound an alarm. Yet while these may have provided adequate defense against the "smash and grab" type of clumsy burglar, they were relatively easy to circumvent. The next generation of glass break sensor employed smaller strips that listened for the vibration caused by breaking glass. The problem was, that particular sound vibration is also mimicked by other sounds, such as the crack of lightning. Even some types of pet birds, it was discovered, could trigger a false alarm.
The researchers returned to their drawing tables to develop a glass break sensor that didn't alert the world to parrot squawks. Finally, they managed to winnow out most other sounds and develop something that would sense breaking glass only. Just don't drop and break a glass in the vicinity of such a sensor: to it, breaking glass is breaking glass.
Eventually, along came the "dual technology" glass break sensor. Operating under the theory that an impact is required in order for glass to break, it needed first that slight noise of contact, followed by glass breaking, before announcing itself. A corresponding improvement in the glass break sensor was that it could guard an area, rather than being attached to every pane.
Like radar, a glass break sensor can't "listen" through a wall or around a corner, but can cover an open area up to 35 feet (10.67 meters). Many of these sensors are relatively inexpensive, less than $50 US Dollars, but keep in mind that coverage for even an average-sized house will probably require multiple units. Also, it is best to at least consult with a home security expert before attempting do-it-yourself installation.