Well, it appears to be a little plastic canister with polystyrene balls in it! Seems a little unnecessary to me.
The Leakfinder by Rema Tip Top helps you find even small leaks in your inner tube or tyre. This little helper with small polystrene balls inside quickly and reliably shows you the spot where air escapes.
Yet, the Leakfinder can also be used to find punctures and holes in air mattresses, paddling pools, rubber boats and other inflatable outdoor accessories. Simply move the leakfinder over the object with the grating facing to the bottom. Once the balls start to swirl around, you have found the leak or puncture.
Hmmm. That's interesting. The picture does indeed look like something that contains small balls.
I haven't had many punctures in recent years. My most recent punctures were caused by chafing of the latex tube, rather than a small sharp object that pierced the tyre tread. The holes were so large I certainly didn't need a leak finder!