Any home-security plan should begin with your main doors. Remember that the back door, especially if it's hidden from street view, can be even more vulnerable than the front. Burglars frequently ring the front doorbell and, if no one answers, go around to the back of the house, where they typically kick in a door, says Bill Robinson, a senior public information officer with the San Diego Police Department.

Dead Bolt

Get a good-quality dead bolt for your exterior doors and you can stop worrying about that credit-card lock-shimmying trick that works not only in the movies but also in real life. Make sure the lock has a bolt that extends at least an inch into the door frame and that the strike plate (the metal piece that mounts to the door frame and holds the bolt) is attached with screws that are at least three inches long. Installing a new dead bolt requires precise measuring and drilling — it's best to call in a locksmith.
To buy: Schlage B360 Single Cylinder Deadbolt, $27, Home Depot, www.homedepot.com.
Installation time: 90 minutes.

Door Guardian Reinforcing Latch

Far more effective than the old-fashioned chain latch, this device screws into your door frame above your doorknob and is easy to install yourself. It has a small hinged bar that keeps your door firmly shut and provides an extra point of resistance if someone tries to force it open. Slim and unobtrusive, the Door Guardian comes in several finishes, including brass.
To buy: The Door Guardian, $28, Ace Hardware, www.acehardware.com.
Installation time: 20 minutes.

Door Reinforcer

This U-shaped metal plate wraps around the outer edge of a wooden door and prevents pry bar-equipped intruders from gouging out your lock. There are models available to fit a dead bolt or a latch-style knob lock (shown here). (Note: A knob lock is not adequate protection on its own and should be used only in tandem with a dead bolt.) Since you'll need to remove the doorknob to install this product, have a locksmith do it when he comes to change locks.
To buy: Mag Security Door Reinforcer, various models, $10.50 and up, www.acehardware.com.
Installation time: 45 minutes.