Unable to create a proximity detector

Thread Starter


Joined Nov 21, 2019
Hello all, I've been searching for hours trying to figure this out between this forum and the internet. I've found I don't even know what I'm searching for because I can't find anything related.

I'd like to figure out how to make a detector that will sound an alarm when I'm too far from my son. Scenario: My son is in his stroller with some device (one of the things I want to build). If I were to walk away for some silly reason and get more than 10 feet away, I'd have a key fob or some other device in my pocket that would alarm to remind to go back and get my son.

Can anyone point me in a direction of what I should be looking for? I've youtubed like crazy key fobs but I don't think that's what I need. I'm just not sure what that is. Any suggestions?

Thank you.


Joined Sep 20, 2005
I am not sure what silly reasons you have to leave your son unattended, but maybe a retractable leash tying you to the stroller would help? ;)

Thread Starter


Joined Nov 21, 2019
How about a 10-foot long piece of string tied to each.
A retractable leash or string is so much less fun and cavemanish. There are many applications for this. What about a proximity of 500 feet? When I was a kid, I had a certain distance from the house I was allowed to go to (some other person's house 10 houses down the street). What if my daughter was playing and went past that? Then I'd be alarmed. There are many others I'm sure.


Joined Jan 18, 2008
Well, if you really must have a electronic system, have you looked into the new, radio-based (e.g., GPS-like) "invisible fence" products?

Then, if you want a DIY, there is u-Blox (https://www.u-blox.com/en/product-search) that makes some very interesting and precise position monitors accurate to a few centimeters. You would need two units, one for the child and one for you. Establish a radio link and constantly compare the two locations. If different by whatever measure you set, it would sound an alarm.

Don't smart phones have position monitors? Maybe there an ap to read and report that?