Securing Windows with Locks
Since glass can be broken, it is harder to secure windows than
doors. Thus window locks are popular options for people who want
to ensure their home is more secure. Levers can easily be
dislodged by outsiders trying to gain entrance, so do not depend
on them for security. Instead, install window locks that can be
secured with a key. Talk to a representative at your local
hardware store to find which lock works best with your type of
window. Chances are you can buy a matched set of locks so you
only need one key to operate all the window locks in your house.
Downstairs windows, being the most vulnerable, should definitely have solid window locks that remain locked all the time (barring sunny days when you're at home and want some fresh air, of course). You should lock upstairs windows as well, though, when you are leaving the home.
Deadbolt Locks for Windows
The most common type of window is the sash frame or double-hung window. Since these windows are easy to pry open from the outside, they should be fitted with a 4-point steel deadbolt that is snuggly secured to the top and bottom of the sash. Another option is pin locks; they can be used in a "hole bored through the bottom of the top sash window and aligned in a hole in the top of the bottom sash window, allowing both windows to be tightly joined" (pg. 22, Personal Security Handbook).
Sliding Glass Door/Window Locks
Sliding windows (this applies to both windows and sliding glass doors) should be secured with a pin and jam in the slide track to prevent the window from being slid open from the outside. You'll still want to use a lock for added security.
Other Options for Window Security
Locks aren't the only means of securing your windows. You can replace the glass in your windows with polycarbonate or tempered glass. Both options are expensive, but they make windows more difficult to break. Some people use security bars to further secure downstairs windows, but this can work against your family in the event of a fire. If you want to feel more secure, you should install a home security alarm system for your home and make sure the windows are hooked up to it via sensors.
Tip: When you're securing your windows, don't overlook the air conditioning unit if you have one mounted in a window. Air conditioners should be bolted to the house in a way that ensures the window cannot be raised and the air conditioner cannot be removed by someone on the outside.
Source: The Personal Security Handbook by Christopher McNab
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