Hi I think this is a great idea
I am one of those parents that would consider using it if it were upgraded but looking at what you have for sale I can point out several reasons why I would not buy it.
Maybe you can relay this info back to the manufacturer
If I were the manufacturer of this product I would change a few things. It would be costly to upgrade however if they did it then they would profit from it. I AM CERTAIN!

#1. I would change the design because it shouldn't be kid friendly. I dont want my daughter playing with this device, if it looks like a toy she will play with it, it is there for her safety. As a child she will try to fiddle with it but she will soon loose interest and find something else to play around with.

#2. What is the device made of? I am a parent and I am looking for something that would not be easy to remove. So, I would want it made of some sort of steel or metal with a lock down on it

#3.This device has to fasten/lock down so that only the parent could take it off with lets say a scan of the parents finger print on the side of it or something similar. Ideas are roaming in my head :)

#4. I would want it in sizes that are attachable to the waist, wrist or ankle and adjustable. I do not want this to be visible to any other person. If I am in the store or at a water park or something like that with my child and a stranger grabs my daughter I dont want that person to see this device. Although it is possible the "JERK" will leave the child alone if the device is seen, its highly unlikely. I think if it is unseen, that will give the authorities/parent time to track my child's device and save her life

#5. This device should carry a tracking device system so that the authorities can track it. Maybe some sort of registration with the authorities when the parent purchases/activates the device.

I know some people are probably thinking why buy this device,
just watch your child! And we do have people that are not responsible but then there are people that are and this device is just one more added security for them and the child.
I would certainly buy this device if it were upgraded and use it for my children and grand children and so on.

GREAT IDEA!
THINK ABOUT IT!