A few months ago I activated a Compass 597 on Ting Wireless with the eventual intent of bashing together a small PIC based solution that used the USB features (though finding a similar chipset that I could miniaturize capable of running code generated by the Arduino software and libraries would have been my preference, I'm not aware of any AVRs that have proper USB support for the necessary USB profiles to get the device to work).
As summer approached, with projects ramping up at work, and Billy demanding more attention and interacting with me more when I'm home (not that I'm complaining, he's really fun to be around and I'm glad he's learning to communicate his desire for companionship and attention to me, even if the means used are sometimes inappropriate), the reality that this would be a project I wouldn't be getting to in a reasonable time period, began to set in. And around this time, I found the Eyez-on EZ120.
I've been researching products for some time, considering organizing to get my community in touch with Project Lifesaver and periodically checking to see if LoJack SafetyNet entered my area (they haven't) (amusingly, people have told me I should put LoJack on my kid, jokingly, and are often surprised to find that LoJack actually does in fact have a product that does exactly this).
More on wandering in my post about this last year here
Anyway, for our needs, Billy typically will not wander away from our property. He makes very few attempts to leave our house (usually the ones he tries for are when he sees the neighbor kid playing outside, or wants mulberries from the tree outside). We have multiple layers of security, extra locks, a baby gate, an alarm system, and a few other things to discourage his attempts. (Amusingly, he is so obsessed with having things be normal that if someone carelessly leaves the baby gate open, he will close it before he realizes "oh man, I could have gotten into the kitchen and raided the snack cupboard!"). Our problem is that if he will typically wander when we are already out somewhere to get away from stimulation or noise, or to go to somewhere that looks interesting to him (at Red Robin today, he ran off and went to the arcade area, and in the past he has run into crowds and run outside in a group of people at Eastern Market). The bear mentioned in the post above serves us well, but I worry that one day he may slip out while we're on a trip, or wander from school (which has happened once before!). For those situations the bear RF based beacon will not be practical, but a GPS beacon would.
Enter the EZ120. It's a small unit, fits in your palm, mostly concealable in the closed fist of the average adult male. It looks fairly weatherproof (but not submersible). The unit is sealed, all switches are depressed and membrane based, and the USB/Charging jack has a rubber plug that goes over it when you're not charging. It's small and light, and uses GPS with a GSM radio chipset to transmit location every 5 minutes, and provides the parent with a mobile webpage they can hit with their cellphone or tablet (it works great on my Samsung Galaxy S4, and my iPad 2). The portal lets you alter some settings as well, such as a speed at which the GPS will instantly alert you (so you can for example be notified if your child enters a car), an option to disable the power button (without that, the only way to get this GPS to shut it off is to submerge it or smash it, there's not an obvious battery cover that I could find), and (most importantly) the reporting interval used so you can set it to report very fast if the child is lost, as you can cover a lot of ground in the default 5 minute interval.
We mounted Billy's GPS beacon on his shoe, as it is the one thing he is consistently wearing when we're out and about, and if we tried to use straps to mount it on his body, it would meet a swift and painful death at his earliest opportunity. The shoe for him tends to be unobtrusive, doesn't affect his ability to walk, and is a visible indicator to grownups that "hey, maybe there's something up with this kid and I should cut him some slack, or stop him if I find him alone". The bear has been an interesting conversation starter, I'm sure a box that periodically blinks is equally interesting).
Thus far, in my experience, the unit has had good coverage in the city and metro areas of Detroit (despite its SIM being from Canadian carrier Telus, the service is advertised to work for no extra charge anywhere in North America, roaming charges apply if used overseas). The predicted accuracy of the GPS (displayed on the portal) is typically 200 feet indoors, and 40 foot or less outdoors. So this isn't a device that is going to help your child if they are lost in a museum (but it will help you find what wing, and confirm they're in the building, which I suppose is a darn good start!) but if they wander outdoors, this will literally save a life.
My biggest worries when I bought it were battery life and coverage, as well as durability, size and overall reliability of the GPS signal.
Battery Life: I'm used to fantastically unrealistic claims about battery life, having used smartphones for 8 or 9 years. So when they said 48 hours, I had a flashback to my Nexus S 4G, and its fabled 7 day battery life (realistically, that ended up being 6-8 hours of battery life, even on a brand new battery. I doubt I could have gotten 7 days on that thing even with the phone in Airplane mode, but I digress). But I was pleasantly surprised to find the device stand up to its claims. While I haven't let it run down fully, I have graphed its discharge rate under typical use (for periods of up to 18 hours so far) and found that it would likely exceed 48 hours by a slight margin, though I expect the dropoff at the last 10 or so percent is pretty severe, like most Li-Ion batteries.
Coverage: The unit, like I expected, is GSM based. (CDMA chipsets for independent developers are hard to come by, and carrier cooperation is even worse) I was concerned it may be on the T-Mobile network, as they historically have been wooing machine to machine developers the longest and hardest. They also don't have the best roaming agreements and tend to charge overage for roaming. Being that the SIM is from Telus, they are likely to have highly superior coverage, as every US carrier that has a GSM network MUST partner with Telus to cover large swaths of the Canadian market, and thus they are likely to reciprocate with every GSM carrier in the US who approaches them. I won't have to worry about the internecine warfare that carriers in the US seem to engage in. Technically, this bad boy is roaming 24/7 as I'm not even in the country where the originating carrier is. I have a feeling that this unit leverages that agreement in a certain way that is low cost or free (such as doing GPRS data, or SMS, or something else that is free/almost free in their contracts).
Durability: While the unit doesn't seem to meet Milspec 810E or IP-67, it seems relatively hardened. As mentioned before, there are membrane buttons or rubber plugs over openings, and the unit feels very solid, made of thick plastic and designed for the kind of abuse a child may throw at it. Billy has kicked tables with it multiple times without any visible impact or damage to the unit.
Size: It's actually smaller than the RF based bear locator. But only by a little bit. The case provided is suitable for our needs now, but there are no direct attachment points on the unit itself. It's designed for wearing on a belt, I used a ziptie to hold it to his fake shoelaces (they're velcro shoes), you could lace it into proper tie shoes without issue. If you want to body mount it, you'll have to find a nylon strap or something yourself, and if your child doesn't want it on, there's nothing in the packaged case to meaningfully impede them from removing it. Fashioning your own attachment method outside of that should be relatively easy given size and weight, a craft oriented person could find a number of ways (including sewing a special pocket into existing clothing) to put it on their child.
Reliability: The unit has never powered off since it arrived. I charge it nightly, and check it periodically on my phone to ensure it is always working correctly. My son has kicked things wearing it, jumps a lot (it's one of his stims) and crawls sometimes, banging his shoe mounted units on the floor. I haven't seen it fail to report in, the provided website seems to maintain good uptime, and I haven't seen periods where the device was in good signal but the website didn't show an update, or showed a delay.
One thing does annoy me – there is a panic button on the device, which my son will occasionally hit as it is visually interesting to him. This triggers a parental alert to our cell phones, and sends us a link with his coordinates. It has no reinforcing feedback on the unit, thankfully, so it doesn't reinforce that behavior by making a cool sound, or anything, and we ignore it when it happens so he doesn't realize it is annoying us and keep doing it. I wish I could disable that feature but it's not a big deal for us.
But i'm glad we bought the GPS, and the $20 a month seems quite fair for what we're provided.
Related news – we got talking to our local police when they responded to a call at our neighbor's house regarding an SUV that swerved off the busy road behind our house, and basically destroyed her garage and car (thankfully missing ours by roughly 15-20 feet, good for both us and the driver as our garage is made of brick, and the neighbor's is wood). Becky asked them what would be a good time to stop by and introduce Billy to law enforcement officers and vice versa, and they got talking and it turns out the officer's kid is also a wanderer, and knew exactly what we were talking about. They apparently will keep records and photograph Billy, and update our file in the 911 dispatch system to inform officers that there is a special needs child in the home. I'm very pleased with that, so Becky will be stopping by in the next week or so to take care of that.