I own a device called a Loc8tor, a handheld device that can pair with multiple RF tags. As you get closer, it beeps quicker. The tags also beep and flashes a little led to make it easier to locate.
I use it to find my cat when it's getting late and he's still not in. It's an very useful piece of equipment.

In the documentation, it claims to have a range of upto 122 metres... Maybe on the clearest day it might be possible, but obviously it's much less than that when used practically, if my cat is hiding in a field of long grass or wheat for instance it's more like ~20 metres. Even so it does the job.

I've just been looking on eBay for some replacement tags. Unfortunately it's hard to come by the original design (a rounded rectangular shape) which fit perfectly to my cat's collar and didn't get in the way, but all that's produced now are disc shaped to be hung from a collar and they're considerably more expensive.

However, while looking around I came across some very cheap RF tags a bit like my loc8tor tags, but they use low energy Bluetooth (they're often titled as GPS trackers for some reason...)
https://www.ebay.co.uk/itm/Mini-GPS...s-Kids-Motorcycle-Tracker-Track-/253675293803

You can use a smartphone and an app to locate them.
But the stated range is 'about 75 Feet', much lower than what the Loc8tor tag and handset purport to be capable of.

But unless I'm mistaken, they both use the same radio frequency, the same battery and (I'm assuming) a very similar type of antenna.
So why is one so much weaker than the other? A quick search suggests it's partly to do with technique and partly to do with power consumption.

I was curious to find more details on how exactly the Loc8tor worked and I came across this freely available patent application:
http://www.freepatentsonline.com/8519906.pdf
In it I found it makes a clear distinction between the technology it uses and Bluetooth:

For optimum high range capability and low power-consumption, the first and second communication modules preferably operate using a specification based on the IEEE 802.15.4 standard. The IEEE 802.15.4 standard uses spread spectrum techniques at 2.4 GHz transmission frequency. The bit rate is 250 kb/s which allows small amounts of data to be transmitted in a short time. In light of the low power consumption
of IEEE 802.15.4-compliant devices, the transceiver device may be powered by a battery of modest dimensions.
Using a specification based on the IEEE 802 .15 .4 standard, the first and second communication modules may have a maximum range of between 100 m and 200 m. For example, the first and second communication modules may have a maximum range of between 125 m and 17 5 m. However, it is conceivable that other suitable protocols (e.g., ZigBee™ or Bluetooth) may be used to implement the present invention.

To my amateurish point of view (I have little to no experience in electronics or RF technology btw) it seems there's very little stopping a standard bluetooth module from operating longer distances if given enough power.

Some questions naturally occurred to me:

Why aren't there any comparable products on the market that use similar RF technology that are appropriately small and low-energy?
Would it be possible to tweak one of these cheap bluetooth modules to use more power, creating a 'bigger' signal?
Leading on from that, why aren't there miniature long-range bluetooth-based locating devices on the market that are compatible with phones?
Regarding the last point, I can think of one reason - in order to have a small, low power consumption tag it needs to be in an idle state most of the time, waiting to hear from a high power bluetooth module before it starts chirping back and consuming considerably more power. But it must be that bluetooth modules in phones are strictly confined to a low power state for short range transmission, making it unsuitable for this.
Would it be possible to modify one of these cheap £2 tags into a high-powered bluetooth handset (with a beeper to indicate strength), probing the airwaves for its little cousins waiting to be located?

It just seems like there's a really cheap solution to this problem that's not yet been implemented.

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EDIT:
I've just been having another look online and I came across a video of someone comparing a 433mhz tracking device with the Loc8tor.

4:00 into the video I was frankly amazed at what I saw.
He mounted the Loc8tor handset onto a parabolic antenna without any modification to the device.
He was able to detect the tag from 7.5km away!
That's a hell of an improvement. I did tests when I originally got mine and it would drop out at about 100 metres with clear line of sight.
I'd love to know how effective it would be in practical circumstances (hedges and trees etc.) but I'm sure it would still prove to be a significant improvement.

Now the thought occurs - what if I bought myself a high gain 2.4ghz parabolic antenna for £50 on eBay, replaced the loc8tor with my phone and the loc8tor tag with a cheap £2 bluetooth tag.
Disregarding the simple impracticability of carrying around a massive radar dish, as if trying to receive alien signals from Mars, is there any reason why this wouldn't prove to be more effective at locating small, low-power bluetooth tags? I'm assuming it would depend more on precision of direction, rather than distance, but for my purposes that'd be an improvement.

 

I can see that you have been doing some thinking about this issue. I don't have any simple answers to your questions, but I wanted to point out one thing:

When you say, "To my amateurish point of view (I have little to no experience in electronics or RF technology btw) it seems there's very little stopping a standard bluetooth module from operating longer distances if given enough power."

Take a step back and consider that "Bluetooth" actually means one of several standards. It is not, in this regard, truly a technology per se.

So, if you want to claim that a module is BLE 5.0 certified, it means, ostensibly, that it conforms to the standard (and all of the requirements of the standard). Such standards allow for the device to be utilized for lots of different purposes by lots of different people. Imagine writing a BLE app on a phone for a device that only sorta kinda was BLE v4.0?

Further, take a look at this article. BLE 5.0 is the newest version and touts the greatest distance, but look how that is accomplished (from the article):

Longer Range
LE Coded PHY is one of the key Bluetooth 5 features. It provides up to 4x improvement in range without increasing transmit power, albeit at reduced data rates. This is accomplished by increasing receiver sensitivity through error control coding on the 1Msps PHY rate (i.e. not applicable to 2Msps PHY rate).

But, what if you only want to build a one-off cat finder for when it is attempting a hostile takeover of the neighborhood? Well, in that case, you may not need to care much about Bluetooth standards because it is a custom situation and you can probably use any kind of hybrid approach that works - which looks like the case with the product that you mention.

Still, it seems that integral determinants of range are transmit power and receiver sensitivity (and a lot of other stuff). Insofar as what your cat is willing to carry around with him for a transmitter, weight (i.e., battery) to power the transmitter is going to be a big consideration. You have more freedom on the other end (receiver sensitivity).

Of course, you do have to be aware of and adhere to regulations - but you can custom design something that could be pretty impressive...or you could just give the cat its own phone and train it to call in every once in a while so you don't worry.