In the 21st century, parenthood and paranoia often walk hand in hand.

For some, the blessed event is followed by high-tech surveillance _ a monitoring system tracks the baby's breathing rhythms and relays infrared images from the nursery. The next investment might be a nanny cam, to keep watch on the child's hired caregivers. Toddlers and grade schoolers can be equipped with GPS devices enabling a parent to know their location should something go awry.

To cope with the uncertainties of the teen years, some parents acquire spyware to monitor their children's online and cell phone activity. Others resort to home drug-testing kits.

Added together, there's a diverse, multi-billion-dollar industry seeking to capitalize on parents' worst fears about their children _ fears aggravated by occasional high-profile abductions and the dangers lurking in cyberspace. One mistake can put a child at risk or go viral online, quickly ruining a reputation.

"There's a new set of challenges for parents, and all sorts of new tools that can help them do their job," said David Walsh, a child psychologist in Minneapolis. "On the other hand, we have very powerful industries that create these products and want to sell as many as possible, so they try to convince parents they need them."

Some parents need little convincing.

In New York City, a policeman-turned-politician recorded a video earlier this year offering tips to parents on how to search their children's bedrooms and possessions for drugs and weapons. In the video, State Sen. Eric Adams _ who has a teenage son _ insists that children have no constitutional right to privacy at home and shows how contraband could be hidden in backpacks, jewelry boxes, even under a doll's dress.

"You have a duty and obligation to protect the members of your household," he says.

Another parent who preaches proactive vigilance is Mary Kozakiewicz of Pittsburgh, whose daughter, Alicia, was abducted as a 13-year-old in 2002 by a man she met online. He chained, beat and raped her before she was rescued four days later.

In recent years, mother and daughter have both campaigned to raise awareness of Internet-related dangers.

Mary Kozakiewicz urges parents to monitor children's computer and cell phone use, and says those who balk out of respect for privacy are being naive.

"It's not about privacy _ it's about keeping them safe," she said,

On a different part of the spectrum are parents such as Lenore Skenazy, a mother of two teens in New York City who wrote a book called "Free Range Kids: How To Raise Safe, Self-Reliant Children (Without Going Nuts with Worry)."

Skenazy, who let one of her sons ride the New York subway alone when he was 9, contends that many marketers exploit parents' ingrained worries about their children's safety.

"The idea is that the only good parent is a parent who's somehow watching over their child 24/7," she said. "You feel nothing should take precedence over monitoring your child's well-being every second of the day ... from time they're born to when they go off to college."

Joe Kelly of St. Paul, Minn., helped his wife raise twin girls (they're now adults) and founded a national advocacy group called Dads and Daughters. Like Skenazy, he bemoans commercial exploitation of parental anxiety.

"Markets play on this fear that something horrific is going to happen to your child, when the odds of that are minuscule," he said. "It might happen, but to have their whole childhood predicated on this remote possibility is, in the aggregate, even more damaging."

Psychologists who work with troubled adolescents and teens say parents often ask if they should be doing more surveillance.

"Ideally, parents establish good open communication and trust with their children, and they don't need to do all these things," said Neil Bernstein, a psychologist in Washington, D.C. "But if the child is doing something to create suspicion, you can't expect parents to turn their back and not monitor."

Bernstein, author of "How to Keep Your Teenager Out of Trouble and What to do if You Can't," says the best approach is a balanced one _ neither overly zealous and paranoid nor uninvolved and neglectful.

A look at some of the monitoring tactics and products available to parents:

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Baby monitors:

These devices _ some limited to audio monitoring, others also with video capability _ have developed a reputation as a mixed blessing. They can provide parents with peace of mind, freeing them to be elsewhere in the house while the baby naps, but sometimes they accentuate anxiety.

"Some parents are reassured by hearing and seeing every whimper and movement. Others find such close surveillance to be nerve-racking," says Consumer Reports, which has tested many of the monitors.

Skenazy likened night-vision baby monitors to the surveillance cameras used by convenience stores and prisons.

"It's treating your child's bedroom as if it's the streets of Kandahar," the battle-scarred Afghan city, she said.

The monitors operate within a selected radio frequency band to send sound from a baby's room to a receiver in another room, a technology which can be vulnerable to interference from other electronic devices. Prices of models tested by Consumer Reports ranged from $30 for audio monitors to more than $200 for some with video.

"Overall, baby monitors can be as temperamental as a 2-year-old," says Consumer Reports. "Interference is probably the biggest complaint, but parents also report such problems as low visibility, a shorter-than-expected reception range, and short battery life."

Models at the high end of the price scale include the Dropcam Echo audio-video system, for $279. Its manufacturer says the system automatically detects motion and sound, and sends alerts to a parent's smart phone or iPad.

Experts say baby monitors can provide a useful early warning if something is amiss, but caution that they should never substitute for adult supervision.

Parents are warned not to rely on monitors to prevent Sudden Infant Death Syndrome, and they should be sure that the monitors' electrical cords are kept away from cribs. Earlier this year, about 1.7 million Summer Infant video monitors were recalled after being linked to the strangulation deaths of two infants.

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Tracking devices:

Of the roughly 800,000 children reported missing in the U.S. each year, the vast majority are runaways or were abducted by a parent. But there are enough kidnappings by strangers _ including a few each year that make national news _ to fuel a large, evolving market for products catering to apprehensive parents.

The devices range from clip-on alarms to GPS locators that can be put in a backpack or stuffed in a doll, but they have limited range and can raise safety concerns of their own.

Ernie Allen, president of the National Center for Missing and Exploited Children, says the devices can be helpful in some circumstances but worries about overreliance on them.

"Some of them encourage parents, perhaps unwittingly, to forget their basic responsibilities," he said. "There are parents who think they can depend on the technology, not on themselves."

He recounted the case of one little girl who activated her wristband alarm when she was abducted. The abductor cut off the device, left it behind and later killed the girl.

Allen said the child might have been better off yelling for help, rather than focusing on the alarm.

"Some of the new technology is extraordinary," Allen said. "But these shouldn't be used as substitutes for good old-fashioned parenting."

Generally, the gadgets are in two parts _ a main device carried by the parent and a small alarm attached to the child. If a child vanishes, the parent can activate the alarm.

Other gadgets use GPS technology, relying on satellite signals, that allows parents using a Web browser to track the location of an enabled device such as a cell phone.

One company, BrickHouse Security, offers a GPS child locater for $200 that functions as a digital watch and can be locked into the child's wrist. If forcibly removed, an alert is sent to the parent's cell phone and email.

Some anxious parents wonder if a satellite-enabled tracking device could be implanted in their child _ a technology now expanding in Mexico among people rattled by a kidnapping epidemic there. But Allen says such implantation, for children, could have grim consequences _ a child who ran away from home or a noncustodial parent who abducted a child might make a grisly attempt to extract the device.

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Spyware:

For many parents, one of the toughest decisions is whether to spy on a child's computer and cell phone activity. It's common for some children to send more than 100 text messages a day, and a recent Associated Press-MTV poll found that about one-quarter of teens had shared sexually explicit photos, videos and chat by cell phone or online.

Walsh, the Minneapolis psychologist, says the best initial step for parents concerned about online risks is a heart-to-heart talk with the child, with monitoring used as a contingency measure only if there's clear justification.

"If it does make sense to use some spyware, I would never do that in secret way," said Walsh, whose own three children are now adults. "Tell your children you'll check on them from time to time. Just that knowledge can be effective."

Mary Kozakiewicz disagrees, saying deployment of spyware must be kept secret.

"You can't let them know it's there, or they'll do it at a friend's house," she said.

Indeed, one of the challenges for some parents is a technology gap _ their children may have more savvy about cyberspace and an ability to thwart various spyware tactics.

"Parents are trying to play catch up _ and it's a highly fragmented, confusing sector," said Keith Jarrett of the AmberWatch Foundation, a nonprofit based in Seal Beach, Calif., dedicated to protecting children against abduction and "the dangers of the digital world."

AmberWatch promotes various safety devices and technologies, including SafeText _ a system enabling parents, for $5 a month, to monitor their children's text-messaging. The system sends alerts when it detects potentially dangerous or inappropriate text messages, so the parents don't have to review vast numbers of messages themselves.

Another enterprise, Software4Parents, reviews and sells a range of spyware products. Its Web site features a comment by Mary Kozakiewicz after her abducted daughter was rescued.

"No matter how you feel about your child or how trusting you are that what's going on is innocent, check it, check it and double check it - or don't have (the Internet) at all," Kozakiewicz warns.

Among the site's featured products are Spector PRO and eBlaster, for sale at $99, and touted as ways way to monitor online chats, instant messages and emails.

"Receive complete transcripts of the web sites they visit, keystrokes they type and more _ all delivered right to your email inbox," the site says.

Several spyware brands, including Mobile Spy and MobiStealth, now offer systems that work with Android, Google's operating system for mobile phones, ranging in price from $100 to $150 per year.

The software "gives you complete control over your child's cell phone," says MobiStealth.

Dr. Henry Gault, who practices child and adolescent psychiatry in Deerfield, Ill., says parents who spy on their children "are walking down a slippery slope" and may end up causing worse problems than the ones that prompted the surveillance.

"That should be the course of last resort," he said. "Essentially you're throwing in the towel and saying there's no trust anymore."

He suggested it's normal for children try to keep some secrets from their family.

"Parents shouldn't feel guilty not knowing 100 percent of what's going on," he said. "It's our job as parents to reduce risk, but you can never reduce the risk to zero."

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Home drug tests:

Compared to tracking and spyware gadgets, home drug testing kits are relatively low-tech and inexpensive. But they raise tricky issues for parents, who may be torn between alienating their child on the one hand and living with unresolved doubts about possible drug abuse on the other.

David Walsh directed an adolescent treatment program earlier in his career and says the at-home tests can be appropriate when parents have solid reason for suspicion.

"When a son or daughter is getting seriously into drugs, one dynamic of that is denial," he said. "The stakes are so high. Parents can say, `We need to make sure you're not doing serious damage to yourself. We might occasionally test you.'"

In Colorado Springs, Colo., single mother Amanda Beihl was among the first to carve out a business from Internet sales of test kits, starting in 1999.

Beihl created homedrugtestingkit.com, selling kits to test for illicit drugs and alcohol use. Individual kits testing for a single drug cost as little as $3; a 10-substance kit sells for $19.95.

It's an ever-evolving field, Beihl says, as teens experiment with new hallucinogens or abuse a range of prescription drugs.

"A lot of parents say they're afraid of ruining their relationship with their kid _ they don't want to be seen as the bad guy," Beihl said. "I tell them, if you're already worried about it, the relationship is probably not that great."

Kim Hildreth, 52, of Dallas, tested both her daughters during their teens. They're now in their 20s, and provide occasional assistance as she runs a company, drugtestyourteen.com, that sells testing kits online.

Hildreth has been in the business since 2003 and says she has many repeat customers _ parents who used the tests on an older child and now worry about a younger sibling.

In Hildreth's case, she opted for testing after concluding that her oldest daughter's best friend was using methamphetamine.

"None of us wants to believe our kids are capable of that," Hildreth said. "Denial is a much more comfortable place."

She also later tested her younger daughter, to the point where resentment surfaced, but said both daughters are now staunch proponents of testing.

"We all think we know our kids, but they can change on a dime, and bad things can happen before you even figure it out," Hildreth said. "They're good at deceiving parents when they want to _ that's kind of their job."

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Online:

AmberWatch: http://www.amberwatchfoundation.org/

Home drug testing: http://drugtestyourteen.com/

Microsoft advice: http://www.microsoft.com/security/family-safety/childsafety-steps.aspx

Consumer Reports advice on baby monitors: http://bit.ly/oUT5Rh

Free-Range Kids blog: http://freerangekids.wordpress.com/

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David Crary can be reached at http://twitter.com/CraryAP