BrewBrain Float wifi hydrometer and thermometer. With this gadget you can track the fermentation process over wifi. Works great for beer, wine, cider, mead and similar.
The device has a rechargeable battery, and is easily charged with a standard micro USB cable. The battery lasts about 6 months when fully charged.
Data from the BrewBrain device is uploaded to Monitor.beer cloud storage, so you can log in and track the fermentation from wherever you want. The service is free and logs all your brews.