This is nothing like the foam floaters that your local boat and/or bait shop used to pass out, no; this thing can keep up to a full kilogram afloat instead of the measly one or two keys of the foam key chains. At a full kilogram, you could almost use this thing to catch fish depending on how big they were.
How it works is that when it and whatever is clipped to it gets dropped in the water, it starts expelling a gas which apparently inflates a balloon that is contained inside. The balloon also has a light in it, and the whole bunch will stay afloat for at least 24 hours.
So, that long of a float time, plus the fact its lit up, and it should be pretty easy to find your lost items as long as you realize they are lost in time, I just wouldn’t go swimming with this thing, it could be a little embarrassing explaining that your shorts were ripped off by an inflating keychain. If you want one they are £12.99, so about $25 USD.