The Apple Watch has a hidden feature for activating Night Shift on the device, a Reddit user discovered recently. If you ask Siri on the Apple Watch to turn on ‌Night Shift‌, ‌Siri‌ will do so, and the display will take on the dimmer, yellow hue that lowers blue light exposure.

It is not clear how long ‌Siri‌ has been able to activate ‌Night Shift‌ on the Apple Watch, but it seems to be recent. Apple has no documentation on ‌Night Shift‌ on Apple Watch, and it was not previously a watchOS 10 option. It's possible ‌Night Shift‌ is tied to watchOS 11, but it is not limited to devices running ‌watchOS 11‌. We were able to use the feature on an Apple Watch Series 9 with ‌watchOS 10‌ installed.

Activating ‌Night Shift‌ can only be done through ‌Siri‌, and there is no toggle in the Apple Watch Settings app or elsewhere on the device. ‌Siri‌ mentions scheduling ‌Night Shift‌ in the Settings app, but that's not an option at the current time in ‌watchOS 10‌ or ‌watchOS 11‌.

‌Night Shift‌ does not appear to be available on all Apple Watch models, with Reddit users unable to activate it on a Series 5 and lower.

The option to suddenly turn on ‌Night Shift‌ without an accompanying setting suggests that it is a feature that has been accidentally introduced, and the toggle could be introduced in a future version of ‌watchOS 11‌ or an upcoming ‌watchOS 10‌ update.

Source: Macrumors