Where the backpack goes, the kid goes. And the associated battery, case, etc would be easier to put on a backpack than on the kid's clothing.

But what scenario do you want to prevent? I think in case of abduction, the backpack would likely be left behind.

People are unreasonably scared of abductions. The most common use case would most likely be to find a kid that got lost.

Of course, this unreasonable fear of abductions means that a commercial GPS tracker for kids would sell much better if it supported the "abducted kid" use case well, on top of more likely use cases.

Backpacks are a mechanism for transporting your belongings in a convenient bag fashioned with straps such that you may wear it, carry your belongings AND have your hands free.

They would typically be worn by the child, and thus a good indicator of where your snowflake is.

But I want to use this to put on BIKES!

> But I want to use this to put on BIKES!

Are you thinking about theft tracking or some other use case?

Sure. It's a valid case. The problem is that it's probably also easily removable, unless you can hide the gps receiver, the cpu, and the long life battery in the bike itself and the necessary antennas (maybe under a sticker say).

Though I have to say I saw a youtube video recently (sorry to lazy to google it) where someone put an apple tracking device in a bike and was able to locate it after it was stolen.

The best place to put a tracker on a bike is in the fork's steering column, since it's empty and open at one end for antennas. Still, it would take a dedicated device, because it needs to fit in an 1" hole.