Apple - How to disable the No SIM Card Installed warning in iPad when using it without SIM?
Ask Siri to "turn off mobile data". Worked for me on an iPad 4 with iOS 10.2. Found in this Apple discussion.
You will need a SIM card to do this. You can borrow one for a brief period.
With the correct sized SIM card, remove the SIM card holder from the iPad, using the SIM card ejector tool (one is provided in-the-box with a new iPad).
With the iPad turned on:
Insert the SIM card into the holder and refit the holder into the iPad.
Go to
Settings app → Mobile Data.Turn off Mobile Data.
Remove the SIM card from the iPad.
Hold down the Power button and slide the on-screen Power Off switch and wait for the iPad to power off.
The next time you turn the iPad on, it will not look for a SIM card so will not give you the SIM card not installed notification
To prevent this message you can continually keep your iPad in Airplane Mode. Whilst not recommended to be on all the time, it provides a solution. If you turn WiFi on you should have no issues using internet features and services.