BLE/RF Leash?

Good day folks,

I've been browsing around the good ol' internet, trying to find out if I'm considering something plausible here, and I think I might be. But that's for you all to help me decide, if ya wouldn't mind helping a newbie out!

So I'm looking to replicate something along the lines of this Child Proximity Sensor or one of these Bluetooth Based Devices (of which there are a few, I only linked to one in particular). I want to create a system wherein one device sends an alert to another paired device if/when they become separated by a specific distance (let's say 25 feet). I have seen plenty of posts around here, and elsewhere, which claim these systems to be entirely unreliable, and even made some out to be a scam of sorts. However, most articles and posts I've found are quite dated, and Bluetooth technology (to my novice knowledge) has come a long way in recent years.

Initially I was planning on using ultrasound and/or IR sensors to accomplish this, but due to their directional nature I can't quite do that without loading a bunch of sensors on each device. Also, unfortunately, it will have to work indoors so GPS doesn't seem to be a reliable option. I know the Bluetooth system I linked to earlier involves a smartphone as the brain, and that is not out of the question here - though I'd rather if I could do without it. If need be it would be ideal to have it as a third device, that maps the distance to the two devices I am monitoring and send alerts to both if the conditions are met. But that's why I'm here, I'm not sure if this is worth pursuing on a moderate budget and just basic knowledge of Bluetooth 4.0. It seems plausible, as does the current alternative of a RF-based system...I just don't know what my next steps are/should be.

Thanks in advance everyone!

It is possible to use BLE to measure distance. However, it is not very accurate, and the RSSI will depend on a lot of other factors. (How many obstacles are between the units, is the antenna covered with clothes, etc. So it all depends pn how accurate you want your system, and how much money wou will pay for it. BLE units are quite cheap.

Thanks for the reply!

I'd heard that I shouldn't expect too much accuracy if I get my measurements from an RSSI-based system, I'd be satisfied if I could locate the objects within a few feet of each other, if that sounds reasonable. The more accurate, the better; though I'm not expecting too much precision. All components should be in open air, without any significant obstacles, so hopefully I can get a bit of precision after all.

Do you (or anyone that happens to be reading this) have any experience with/recommendations for BLE systems that are compatible - or easily modified to become compatible - with Arduino? I currently have an Uno but it seems as though a Yun is more geared towards wireless projects, if I'm not mistaken, so I may have to invest in one/some of those.