An electronic home-security system is the single most effective way to deter a potential intruder. But it’s expensive, with some costing upward of $3,000 just for hardware and installation.

Though not as effective as an alarm system, a sturdy door lock can nonetheless be an able deterrent. And at prices ranging from $20 to $200, they’re considerably cheaper.

We recently tested more than two dozen locks for their resistance to picking, drilling, sawing and kicking. (We sawed through deadbolts, and simulated a burglar’s kick by swinging a heavy metal pendulum at doors.) Most of the locks provide at least good kick resistance when installed as is. Several that faltered, meanwhile, were significantly strengthened by replacing the supplied strike (the metal plate that’s mounted on the door jamb and into which the lock’s bolt slides) with an after-market product.

Our tests covered five types of door locks.

¢ Single-cylinder deadbolt. These have the familiar thumb-turn handle on the inside knob. Although inexpensive and relatively easy to install, they’re not the best choice for doors with glass that could be broken by an intruder, who then reaches in and unlocks the door.

¢ Double-cylinder deadbolt. Instead of a thumb-turn handle, the inside portion of these locks has a key slot, same as the outside. They’re more secure than single-cylinder locks for doors with glass in or around them, but the inside key needs to be readily accessible for a quick escape.

¢ Surface-mount deadbolt. These D-shaped locks are mounted on the back of the door. While they’re less susceptible to being opened by hammering and sawing than other types of locks, their housing may seem bulky and obtrusive. And they can be difficult to install.

¢ High-security deadbolt. The most expensive locks, these have unique pin configurations and hardened cylinders to resist picking and drilling. Since most don’t allow unauthorized key duplication, it can be inconvenient and costly to get copies made.

¢ Handle set. These are similar to a standard cylinder deadbolt, but an ornamental handle inside and out replaces the key-in-knob lockset. Handle sets cost more than a stand-alone deadbolt, yet provide no more security.

If you’re concerned about thieves who drill and pick – as well as kick – we recommend two Medeco high-security models, both excellent performers as sold. The Maxum Residential RL-011101 ($160) is a single-cylinder lock. The double-cylinder Maxum Residential RL-016100 ($200) is a better choice for doors with glass. Although not quite as resistant to battering as the Medecos, the Assa V6000 ($160) is a very good single-cylinder high-security lock that offers excellent protection against picking and drilling.

Locks that, out of the box, offer excellent kick-in protection (though poor defense against picking and drilling) include the Weslock 671 ($25) and the Emtek Low Profile 8455 ($25). Both are single-cylinder deadbolts that also provide excellent resistance to sawing. Available primarily through locksmiths, they are CR Best Buys. If your door or jamb has glass near the lock, chose the double-cylinder Kwikset UltraMax Security 985S ($50).

Highest-scoring among handle-set locks we tested was the Kwikset UltraMax Signatures Chelsea ($100), which is highly kick resistant as-sold (though not much good against drilling, picking or sawing). Our sole surface-mount lock, the Segal 666 ($50), provided very good kick resistance and excellent defense against sawing, but was susceptible to picking and drilling.

Several other locks we tested showed improved kick protection with the substitution of a sturdier box strike. (We used the Mag Security Box Strike, available at Home Depot for $10.) Another inexpensive way to enhance a new or existing door lock is to replace short mounting screws with 3-inch ones. Screws of that length will penetrate the thin door jamb to reach the studs, providing more resistance to impact.