In iOS phone 'Settings' > scroll to & tap 'Control Centre' > tap 'Customise Controls'. From here you can add 'Controls'. Add 'Do Not Disturb' (the car icon) by tapping the + symbol to the left.

For Android phones > add the new 'Android Auto' app from the Google Playstore > follow the set up tips & instructions to send auto-responses. Not only can you add the 'Out of Office' auto-repsonse feature, you will promote safe driving.

When 'Do Not Disturb' is switched on, any calls you receive will go straight to voice message, you need to make sure that you have recorded a suitable message.

In iOS > swipe up from the bottom screen to show the ''Control Centre' > tap the 'Do Not Disturb' icon to activate/de-activate.

In the free 'Android Auto' app, you manage all settings in the 'Menu' (hamburger) via 'Settings'. 

There are lots of features in this app for safe driving and automatic detection with certain car models, car stereos, Bluetooth and screens.

In iOS phone 'Settings' > tap 'Do Not Disturb' (crescent moon icon) > scroll to and tap 'Activate' then choose 'Manually' > scroll to 'Auto-Reply To' > then tap 'All Contacts'. 

Still in 'Do Not Disturb' > tap 'Auto-Reply' > type your personal 'Out of Office' response.

In 'Do Not Disturb' mode, your contacts will receive your 'Out of Office' message & a 2nd auto-message '(I'm not receiving notifications. If this is urgent, reply 'urgent' to send a notification through with your original message.)'

You can then turn the 'Do Not Disturb' on and off through the swipe up 'Control Centre'. Don't forget to change the auto-response message if you need to.

For Android enter the 'Android Auto' app > tap 'Settings' > scroll to 'Notifications" then tap 'Auto-reply' >  type your personal message > tap 'OK'. You also have other options, such as swiping the 'Always preview message' & the 'Show message notifications' toggles.