For five minutes, Kim Gavin lived every parent's worst nightmare. Three years ago, she and her husband took their two daughters to a playground party place -- a mish-mash of different inflatable play areas and bounce houses in a single, massive room. No adults were allowed inside the children's area, but Gavin was assured that the area was enclosed. So she kept a loose eye on her kids from a distance. But then Gavin didn't see her youngest daughter, who was 3 years old at the time. She informed her husband, who didn't see her either. The panic started to set in.

"At first, you worry, 'Is she trapped underneath something?" Gavin said. "And then you worry, 'Did somebody take her?' It was my first real experience losing a child, and it was horrifying."

As it turned out, the play area wasn't as enclosed as everyone had thought. Her daughter had squeezed her way out and into the building's lobby, where an employee pulled her aside and kept her safe. But those five minutes of helplessness inspired Gavin to take action; were this to happen again, she wanted to be more proactive.

Gavin is a technical consultant for a medical-device company, so she sought out a technological solution. She took inspiration from the Tile tracker, which uses Bluetooth beacon technology to locate people's wallets and keys. By December 2016, Gavin had a working prototype for Monkey, a product that relies on beacon technology instead of GPS to keep children safe. It debuted at CES in January.

Parents can use the Monkey app to set a range for the child -- most opt for the 15-to-30-foot range. The smartphone then serves as a beacon: As the child moves farther away and the signal gets weaker, the status of the "monkey" will turn from green to yellow to red. The app will set off an alarm to alert the parent that the child has moved out of range.

"Typically, beacon technology is lower cost than GPS," said Steven Statler, who hosts a beacon-technology podcast and is the senior VP of marketing and business development at Wiliot. "You can also make it really small, even the size of a guitar pick."

The Monkey tracker is a preconfigured RadBeacon Dot; its radio board is incorporated into a kid-friendly exterior and attached to the child's shoe. The form factor was something Gavin worked on for more than six months. It needed to be something appealing to boys and girls, and tolerable to wear. Gavin considered a lanyard and even a clunky bracelet before settling on the current design.

"Monkey is for that critical 1-2 minute range of when kids start to go wandering," Gavin said. "The average child wanders approximately 300 yards from their parents, so I wanted something that would work closely and in real time. The beacon was perfect for that."

Because beacon technology is a local connection between the beacon and its recipient, it uses considerably less power than GPS, which triangulates signals from satellites in space to get its bearings. And because most parents will use this technology on the go, they will need to consistently charge their phones for GPS to be constant and effective.

"One of the horror stories [among developers] is that you put all this effort into having people download your app and install it," Statler said, "and then, once they find that the power on their phones is being run down, they'll uninstall it.

"Unlike GPS, beacons also work when indoors," Statler continued. "If you're in an environment like a classroom or a shopping mall, you're out of luck."

One needs a clear view of the sky for GPS to be accurate and effective. Otherwise, there could be up to a three-to-four-minute delay -- precious time in the event of an abduction. Bracké concedes this point, noting that GPS trackers will log the last known outside location -- usually the entrance to a building -- so a parent will know where a child went. It would then continue tracking the child if he or she were to head back outside. Bracké points that beacon tracker apps also have limits.

"They are alerts, in principle," said Bracké. "They can tell you that you have lost something. But if you want to know where, you can't, because it's already gone."

Trax plans to integrate Bluetooth technology into future models -- that way, the devices can have the best of both beacon and GPS technology: precise location at a close distance and real-time tracking from afar. Its upcoming Trax LTE Cat M1 model, due out by late 2018, will include this plus wireless charging.

Monkey, meanwhile, is a budget option that executes one strategy -- proximity tracking -- very well. It is available on iOS and will available on Android by the end of May. For future models, Gavin wants the tracker to have a real-time "distress signal" where the beacon vibrates and notifies the child when he or she has stepped out of bounds. She also wants to leverage the new Bluetooth 5.0 technology to expand how far the tracking will reach. Gavin anticipates launching the second-generation Monkey device in late summer.