The Mudra Band is not an ordinary third-party strap for the Apple Watch. Wearable Devices Ltd claims to have brought gesture controls to the popular smartwatch by way of interpreting nerve signals. The Mudra Band communicates via Bluetooth and is currently available to order for US$159. The project has raised over US$170,000 in crowdfunding so far, too.
https://www.notebookcheck.net/Mudra-Band-Gesture-control-wristband-for-the-Apple-Watch-raises-over-US-170-000-in-crowdfunding.485204.0.html