REDMOND RFT-08S

1) very small and lightweight
2) availability of reliable fastening
3) many additional functions (turning on the camera on a smartphone from it, detecting the movement of an object / animal to which the tracker is attached, measuring the battery charge inserted into the tracker, and even measuring the temperature)

1) not recognized by any mobile device (see comment)
2) range of up to 50 m
3) sometimes semi-dead batteries included (see comment)

I bought 2 copies at once as a gift to a friend who has 2 dogs.
I decided to test it first. I found in each package with the tracker 2 CR2032 batteries made in China. With those that were inserted into the trackers, the trackers showed no signs of life (however, there is a mention of this in the instructions). Of the other 2 batteries, one was in the package, the other was not. The first has a charge of 100%, the second only 30%. The charge is determined by the Ready for Sky application.
Installed Ready for Sky on Lenovo A606 smartphone with Android 4.4.2 on board. The application did not detect either of the two trackers, although, judging by the attached instructions, everything should work starting from Android 4.3.
Installed Ready for Sky on a Samsung Galaxy Tab A tablet with Android 8.1 on board. Trackers are discovered and work.

Can't forget keys, good signal, normal range

Fragile, I'm afraid to crush in trousers

With a smile, I remember how I forgot both the keys and my work purse at home. Now the family and the wife have it, it is attached to the car keys so as not to go up to the 17th floor 2 times (often the elevator is broken). The range is quite enough, and I don't have such a large apartment. Has one fear - I'm afraid to crush in trousers, it seems fragile.

Size, price, and quick detection of lost keys

No them

For keys that I often forget and where I don’t remember - the very thing. Another plus is that it precisely determines the temperature in the room and how a reminder can help out, a useful little thing and works well