We'd have put money on IK Multimedia being one of the first major music software developers to release an Apple Watch-compatible app, so it's no surprise to see that the company's UltraTuner has been made wrist friendly.
Assuming you've got the latest version installed on your iPhone, you can use the Watch to help you tune your guitar. In Stage mode, you'll see two large yellow LED-like wing arrays that light up in progressive amounts according to whether the note played is flat or sharp, while in Note mode, you'll see the letter name of the note currently being played and arrows below indicating whether it's flat or sharp. The note name turns bright green when it's in tune.
UltraTuner is available now from the Apple App Store priced at £3.99/$4.99.