Most burglars enter homes by simply opening unlocked doors or windows—or pushing and kicking locked ones until they open. Bad guys prefer unlocked doors and windows; however, many can quickly and quietly pry open locked ones. Some break a pane of glass and reach in to unlock the window or door. Only a few really determined burglars break out enough glass to walk or crawl through, bash in well-secured doors, or pick locks.

Here are steps you can take to beef up your home’s physical barriers.

Lose Lousy Locks

Good locks are essential. Click here for info on various types of locks, how they can be strengthened, and how to find a good locksmith.

Secure Sliding Glass Doors

The locks on sliding glass doors are notoriously flimsy—many doors can be lifted right off their tracks. If you have one, consider paying a locksmith to evaluate its vulnerability and, if necessary, install reinforcements.

With most models, one door is fixed (screwed or bolted at several points to the track) so you just have to worry about its partner. You can prevent a pry-bar attack if you place a broomstick or piece of lumber in the lower track to prevent the door from sliding open. Aluminum “Charley Bars” mounted waist-high function the same way. Well-designed ones ($20 or less) require moving one or two parts before they can be lowered, making them somewhat more resistant to persistent intruders than wood in the track.

If both doors slide, secure them by drilling two 9/32-inch holes where their frames overlap at the top and bottom. Drill through the inside door’s frame and halfway into the outside door’s frame; then insert 1/4-inch bolts in the holes. This will prevent intruders from prying the doors open and make it difficult for them to lift them off their tracks.

To prevent burglars from lifting a sliding door off the track to open it fully, drill vertical holes through the overhead track every 12 inches or so. Drive screws into these holes just far enough so that the doors slide under their heads but can’t be lifted off the track. (Note: This technique will not work on some hollow frames.)

Replace Weak Doors

Although hinged doors are much safer than sliding glass doors, intruders can get through even securely locked ones.

Hollow wood doors can be easily punched through. Exterior doors should be solid wood or foam-filled metal. And for outward-opening doors, choose ones with hinges that have non-removable pins. Hinges should also be installed so that the screws attaching them to the door and frame cannot be removed when the door is closed. Doors should fit snugly within the door frame, with no more than a 1/16-inch gap on either side. Click here for ratings of door installers.

The last word in door security is a heavy-duty steel door in a steel frame with a high-security lock. These cost $800 to $2,000, installed.

One step down are metal bar doors installed a few inches outside an existing door. They are set into a brick or concrete block structure, and defeating them generally takes a lot of time and makes a lot of noise. Their resistance to attack depends on the strength of the framing to which they are attached. The simplest kinds of metal bar doors, which are usually installed along with bars over the windows, make your place look like a penitentiary. But some fabricators make attractive decorative or even artful ones.

Fix Your Windows

There are five common types:

  • Double-hung (sash) windows open vertically; sometimes the top half is fixed and sometimes not. Frames may be wood, vinyl, or metal.
  • Horizontal sliders are like small sliding glass doors and usually have metal frames.
  • Casement windows swing outward and are usually opened and closed by a lever attached to a geared hand crank.
  • Jalousie windows are a series of panes about four inches wide set in metal frames interconnected by levers.
  • Fixed pane windows do not open.

Secure windows by making them resistant to being pried open. In addition, it should be difficult to open the window frame after a pane of glass has been broken. Most intruders are not keen on breaking glass, but it still happens often enough to justify concern. For the highest level of protection, the window should have unbreakable glazing or steel bars across it.

Quick Fixes

The most difficult-to-secure type of window is the jalousie, since its panes are easy to remove, even when the thing is locked. If you have a vulnerable one, consider replacing it, adding bars, or attaching an alarm to it.

Casement windows, when closed, often withstand break-ins due to the locks on their frames and their hand crank mechanisms, which resist prying. Still, if you leave one open a few inches, someone can reach in and turn the crank to fully open the window. Make that more difficult by removing the handle or cover the window with bars or an alarm screen.

Because locks on horizontal sliders are often flimsy enough to be snapped, consider auxiliary locks.

Double-hung windows are relatively easy to secure, but many commonly available locks are not effective. A simple way to secure them is to pin the two frames together.

Improve Glazing

You can make windows even more secure with impact-resistant glazing, such as Plexiglas or Lexan. Premium grades of these plastics are virtually free of visual distortion and more resistant to scratches. Just make sure you or an installer follow manufacturers’ instructions for mounting them, since temperature increases make them expand more than glass, and intruders can bash in an entire improperly mounted pane.

At considerably greater cost, you can have a pro replace particularly vulnerable windows with the type of glass used in car windshields, which is not difficult to break but hard to remove.

Install Bars

Protective metal bars are the ultimate break-in deterrent. These bars (also called grates and grilles) come in straight prison-issue and various decorative versions. Most are fully welded on a semi-custom basis by local installers who do not sell them for do-it-yourself installation.

Hardware stores, however, often stock bar sets ($20–$80) that can be adjusted to fit your windows; they come in several heights and expand up to 42 inches wide. They won’t resist attacks as effectively as fully welded bars, but properly installed they’ll discourage all but the most determined intruders. Some hardware stores also stock fully welded window bars, although the selection is limited and may not be suitable for your windows. If the width doesn’t fit exactly, you can cut the fasteners with a hacksaw.

Both expandable bars and fully welded bars should be installed with large one-way screws—or with carriage bolts, as long as they are punched with square holes and the nuts would not be accessible to intruders.

Bars should be secured with bolts or screws positioned parallel to the wall, and then welded to the bars. This makes it very difficult to remove the fasteners and pry off the bars.

Professionally installed, fully welded bars cost about $100 to $300 for a 30-inch-by-60-inch window if you get bars for several windows at one time.

Don’t Block Escape Routes

Metal bars on windows or doors, or difficult-to-remove locking devices (such as screws in window frames), pose hazards in the event of fire. Most building codes specify that any sleeping room without an exterior door should have an easily opened window. Window bars with hinges on one side and a lock on the other are risky because the keys can easily be misplaced. Hinged bars with an extended mechanical latch release are safer: No one outside can reach the release, but it can be easily operated by someone inside.

If windows are secured with screws, make all occupants aware that to escape through the window they’ll need to knock out the glass, place a blanket or other padding on the bottom frame, and carefully climb out. Even then, escape through broken glass will be hazardous.

Block Other Access Routes

Intruders love unlocked attached garages. After entering the garage and closing the door, they can then bust into the house unseen and unheard.

Standard twist handle locks on overhead garage doors can be easily defeated. Most electric door openers provide more resistance, but because even these may yield to a crowbar attack, it’s good to have a backup lock. One simple and inexpensive solution is to drill holes in the track on each side just above the closed door and put U-bolts or padlocks through the holes. This keeps the door secured only from inside the garage when the door is closed. The door can also be secured from the outside with a hasp and padlock.

In search of hidden entries, many intruders head to utility rooms and enclosed porches. Make them difficult to access. Plus, make sure a solid-core door with reinforced locks separates them from the rest of your house.

If someone could conceivably enter your attic from the outside, lock the attic hatch or door. Instead of glass, most skylights are now a thin plastic that is easily broken. Consider shatter-resistant glazing or adding metal bars.

Most window air conditioners can be removed easily from the outside or by pushing the unit in. The first precaution is to secure the partly raised window frame tight against the A/C case by pinning or screwing the frames together. The easiest way to prevent someone pushing or pulling out the unit is to screw a piece of lumber to the top of the windowsill. You can improve the aesthetics by extending the board from one side of the frame to the other and painting it the same color as the sill.