The first step in making any home security plan is to assess your locks.

All exterior hinged doors, including doors leading to a garage, should be equipped with good deadbolt locks. Key-in-the-knob locks are inadequate for security because they usually can be quietly shimmied open in a few seconds. Although this can be prevented by bolting a guard plate to the outside of the door, these locks still can be defeated by other means.

There are four basic types of deadbolt locks:

  • Cylinder deadbolt (also known as “tubular deadbolt”). Standard equipment on many houses since the 1950s (see left half of the figure below), cylinder deadbolts have a substantial portion of the mechanism located within the door. The latch is a horizontally movable bolt that extends into the strike plate on the doorframe; it is controlled by a key in a cylinder on the outside and by a thumb-turn on the inside. When engaged, the bolt should extend at least one inch beyond the door. Also, unless a heavy beveled collar extends out from the door on the outside, it may be easy to defeat. Ordinary cylinder deadbolts cost $7 to $75 or more, and $100 to over $400 for fancy electronic models that are unnecessary for most residential uses.
  • Interconnected lockset. This is a combination of a key-in-the-knob lock and a tubular deadbolt (see right half of the figure below). The interconnect device is hidden, but turning the thumb-turn opens both the deadbolt and the key-in-the-knob latches, a feature designed to facilitate quick exits. These locks are installed in six- or eight-inch-high hollows that weaken doors. If you already have good deadbolts, we advise against replacing them with interconnected locksets, even if you like their quick-exit features. They usually cost $30 and up.
  • Surface-mounted deadbolt (also known as “rim-mount lock,” “knuckle-lock,” or “vertical deadbolt”). This ugly contraption has most of the mechanism built into a casing that attaches to the interior side of the door (see left side of the second figure below). Easier to install than tubular deadbolts and generally stronger, surface-mounted deadbolts range from $10 to more than $40.
  • Horizontal deadbolt (also known as “horizontal rim lock”). This is similar to the surface-mounted deadbolt except that its latch moves horizontally (see right half of the second figure below). If the latch extends out at least one inch, these locks can be quite effective.

All four types of deadbolts usually come with a keyhole on the outside and a thumb-turn on the inside for setting and retracting the bolt; this is called a single-cylinder lock. If you have a glass door, or glass panes in a wooden door, or glass near the door, consider the double-cylinder version. This replaces the inside thumb-turn with a keyhole that can be turned only with the key, even from the inside.

The trouble with double-cylinder locks is that they are less convenient to relock after entering the house, and can be a real hazard if your family must make a quick exit in the event of a fire. Because of this risk, some jurisdictions prohibit double-cylinder locks on exterior doors. If you install a double-cylinder lock, hang a spare key somewhere nearby (in a place that cannot be reached by potential intruders), and have your whole family practice locating the key and opening the door while blindfolded (smoke from house fires often creates near-pitch-dark conditions).

There are several alternatives to double-cylinder locks. You can replace the glass with shatter-resistant glazing, or back up the glass with shatter-resistant glazing. You can wire the glass to an alarm or, if glass is built into the door, replace it with a solid-core door.

Good deadbolt locks deter most thieves—as long as you keep them locked—but diligent bad guys can exploit their weaknesses. Fortunately, with modest effort you or a locksmith can reinforce deadbolts—

  • Some vertical and horizontal deadbolt locks come with puny screws. Substitute the longest, thickest steel screws that fit.
  • The cylinders on many locks can be picked or otherwise defeated. High-security replacements are available for $80 to $200 or more.
  • Most cylinder deadbolts and some interconnected locksets have weakly secured strikes for the doorframe, usually secured with two 3/4-inch screws. Replace these screws with two- or three-inch ones. An even better solution is to replace the regular strike plate with a “security strike” or “strike box” that has holes for additional screws. One type is about six inches long and has holes for four or six screws; make sure holes are at least one inch apart. Another type has a metal cup welded to the plate (into which the bolt protrudes) and extra screw holes in the bottom of the cup (see the figure above). Most stores sell security strikes for $2 to $10.
  • To install tubular deadbolts, two large holes are drilled in the door—one for the cylinder-and-lock mechanism, and one for the bolt. The holes weaken the door, but you can reinforce the door by installing a metal door channel (see the figure below) around the door in the area of the lock. Brass-plated channels cost $10 to $40. Avoid channels that are less than eight inches high.

Relatively handy homeowners should be able to install most types of locks. If you want to go it alone, you’ll need one or two special drill bits to make large-diameter holes with a 3/8-inch electric drill. Most homeowners should be able to add a vertical or horizontal deadbolt lock to a basement door, or a back door that does not need to be unlocked from the outside, by using a small bit to drill the screw holes. Discard the through-the-door cylinder assembly and retainer plate, and mount the rest of the lock on the inside of the door, as it would normally be installed.