We'll never know who pawned that copy of Angela's Ashes at a New York bookstore, whether the person was male or female, minor or adult. But with one swipe of a new drug test across the paperback cover, we learned something infinitely more private: the previous owner likely endured the McCourt clan's Limerick woes with the aid of Marijuana.

Drug Detector, which offers America's first over-the-counter tests for marijuana and cocaine residue, requires nary a strand of hair, drop of saliva, or jar of pee. Sold by American Bio Medica of Kinderhook, New York, the product promises to make drug testing a nonconfrontational pastime. Instead of begging a child to submit to an invasive sample-based test, parents can now covertly slip into their son's or daughter's room and instantly discover whether microscopic specks of herb or blow dot the desk, drawers, or pillowcases.

Teenagers don't tell their parents when they're using drugs," says Stan Cipkowski, the company's founder and CEO. "And most parents don't have the kind of relationship with their kid-or the balls-to simply go up to the kid and say, 'Here, pee in this cup. I'm going to test you right now.' "

Since 1996, American Bio Medica's flagship product has been Rapid Drug Screen, a kind of dipstick urinalysis test popular with emergency rooms and drug-free workplace programs. But since it relies on human biological material, Rapid Drug Screen faces a lengthy FDA review before it can be marketed to retail customers.

Fortunately for the company, a firm called Mistral Security, a specialist in explosives detection, had created a drug-residue test for which it had little use. American Bio Medica licensed the invention, which needed no federal approval, and began packaging it for drugstores and online shoppers. Kits have been available at www.americanbiomedica.com since June, and Cipkowski predicts that Drug Detector will begin appearing in major-chain pharmacies by the beginning of next year.

A Drug Detector pack contains 10 matchbook-sized papers and a small, chemical-filled aerosol canister. Simply wipe the suspect surface with a collection paper, spray it, and wait for a color change. A positive result for marijuana is indicated by the rapid appearance of reddish brown dots; for the cocaine version, blue spots suggest that minute traces of nose candy are in evidence. At $34.95, or about $3.50 per test, Drug Detector is far cheaper than such laboratory staples as urinalysis ($10 to $12) or hair analysis ($60). The company also plans to sell an "industrial" version of the kit, containing papers and sprays for methamphetamines and opiates.

Despite the low price, American Bio Medica claims that Drug Detector is as reliable as any law-enforcement diagnostic device-somewhere in the neighborhood of 98 percent accurate. False positives can occur when uncontrolled substances such as nutmeg or henna are present, but the company claims such instances are rare.

In nonscientific field tests conducted by the Voice, the product was, indeed, able to detect the presence of Mary Jane residue on the freshly polished desk of one habitual blunt smoker, while giving an appropriately clean bill of health to the elevator doors at 10 Rockefeller Plaza. A copy of the Allman Brothers' eponymous 1973 album, recently purchased at a street fair, surprisingly tested negative for marijuana residue. At least one naughty patron of Chelsea hot spot Serena apparently used the men's room sink to powder his nose; the loo at nearby cop hangout Peter McManus was pristine.

American Bio Medica is quick to point out that should a child's backpack, jacket, or computer keyboard test positive, the result should not be considered absolute proof of narcotics use. "You can determine at least if there have been illegal drugs in his immediate area," says Brittany Johnson, the company's national sales manager. "That doesn't mean this person has used drugs, just that they have been exposed. A voluntary follow-up with a Rapid Drug Screen allows you to determine if he's using."

Civil libertarians, predictably, bristle at the concept of behind-the-back checkups. Louise Roback, director of the New York Civil Liberties Union's Capital Region chapter, vehemently objects to the test's inability to differentiate between contact and use. "If you're going to use that for a basis to terminate someone," she told the Albany Times Union in June, "it's a basis for concern."

Though its Web site pitches Drug Detector for use in the workplace, the company emphasizes that the primary market is not businesses but parents. "We feel the value of the service that is provided to consumers, especially parents, outweighs the privacy issue in most cases," says Johnson. "Keep in mind that the parents who are going to use this product aren't trying to hurt their child or take away their rights. They are trying to gather the right information so they can open a dialogue with that child and get them the help they need so they can live to see adulthood." To that end, each Drug Detector kit includes a questions-and-answers brochure that provides contact information for Phoenix House and the National Council on Alcoholism and Drug Dependence, as well as the aphorism "Remember, you are not a bad parent."

Rave habitues have also expressed reservations, bombarding the company's Web site with negative feedback. "Their opinion is that we're bleep bleeps, bleep bleeps," says Melissa Decker, investor relations manager. "They say, Why are we bothering a society that we don't even know about just so we can feel comfortable at night and we can go home to our nice houses and our nice dogs? Why don't we bother the crackheads on the corner that are shooting kids?" The company's response: "We thank them for their comments."

Cipkowski acknowledges that misuse is possible, perhaps by "some supervisor who has a vendetta against an employee, or some parent who is overly paranoid." But he maintains that Drug Detector's lifesaving potential far outweighs any ethical sticking points. More importantly, with an estimated 15,000 teens trying drugs for the first time each day, a financial bonanza awaits. "We're here to make money for our shareholders, number one," says Cipkowski. "The fact that we're selling a product that we think is going to help in a parent-child relationship, that's number two."