The only downside to the Amber Alert is its price. The device sells for $200, and it requires a service plan, $14.99 a month for basic tracking features, and $24.99 a month if you would like extras, including voice-calling and sex-offender alerts.

Securus eZoom

Another child-tracking device I tested, the Securus eZoom, is slightly larger than the Amber Alert and doesn’t have some of that device’s features (like voice calling), but it is also significantly cheaper. The eZoom sells for $99.99, and its monthly plan is $19.99. If you pay for two years at once, you can bring that down to $12.99 a month.

Securus also makes a couple of GPS devices for other uses. The eCare is meant for seniors who need medical help. In addition to tracking, it has an SOS button that puts in a voice call to an emergency call center. The eCare sells for $99.99, with a $29.99-a-month service plan.

Securus’ dog tracker, called SpotLite, is a water-resistant 2-ounce module that hooks onto your pet’s collar. (The company says the device is best for dogs weighing more than 10 pounds; it’s not recommended for cats because of its size.)

The Spot

Then there is a GPS device designed for keeping track of your most important possession: yourself. The SPOT Satellite GPS Messenger, which sells for $119.99 and requires a $99-a-year contract, is meant for adventurous types who routinely wander far off the grid.

If you find yourself in an emergency in a place without any cellphone connectivity, you can hit a button to alert rescuers to your location; the device works almost anywhere in the world as long as you have a clear view of the sky. If you’re not in trouble, you can use the SPOT to send a message letting your friends know you’re fine. They can also track your progress across the Outback on a map. The SPOT has led to dozens of rescues, including two people whose plane crashed into the Gulf of Mexico early in October.

Both Securus’ and Amber Alert’s services allow you to monitor multiple trackers at once. If you have many children and an ailing mom and a dog, you can watch them move about town on the same map, a kind of air-traffic control panel of familial concern.

As you’re watching this map, there’s a possibility you’ll have second thoughts about what you’re doing. Are you being a little paranoid? Do you really need to keep track of all these people (and pets) in your life? And what about your children’s privacy and personal space: Isn’t GPS tracking enabling helicopter parenting?

But the chief executives of both companies argue that GPS tracking can actually help parents avoid acting overly protective. Even though most statistics show that rates of violent crime against children have declined significantly over the past few decades and that abductions are extremely rare, it’s hard for some parents to get over the fear of letting children wander out into the world.

A GPS tracker can help parents conquer that anxiety: Because you know you’ll be able to find your children when they’re in trouble, you might allow them to walk to school, take the train to the movies or do any number of other grown-up things that children today don’t get to do.

What about your child’s privacy? Amber Alert and Securus both recommend that parents don’t hide the trackers from their children; indeed, the trackers work best if children know that they can use them to alert their parents during an emergency. Privacy becomes more important to children as they get older, but at a certain point they might consider trading their privacy for freedom.