I bought one for my cat, never did help with finding him, just the general area.

They're not great for tracking things that move on their own, or things that avoid people.

We use them on our cats and have found the trouble-maker cat 3 times out of 3 when needed (in an urban apartment area; most recently the cat was scared by a noise which may have kept her hidden out all night in the cold, unless we had found her/shooed her back to the house)