wifi lost and closing tablet

I've a MIT App in a public place and I would like to avoid people go away with the tablet !! ;-)

I thought about this : if ppl is far away from our wifi network (e.g. outdoor), a message will tell him/her he/she has to bring back the device.

To do that, I've used the Sensor Component and I've set LocationSensor1.ProviderName to "Public" (it's the name of our public network and the tablet will be wifi enabled).

I thought use Call Notifier1.ShowAlert notice "Wifi Lost" 

Do you think it's a good method ?

More important: I would like to stop the use of the tablet once wifi is lost. I would like to have to enter a password to reinitialize the device ...

How can I achieve that ?

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Nothing works as well as a physical chain. There are undoubtedly good tablet holders that prevent people from taking it away, as you can see in many shops.
Also there are protection programs, like find my tablet etc. Google for them.
App Inventor cannot be Of much help, because it cannot run in the background, therefore a thief could just stop the app and you would not notice.

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Thanks for your reply. I'll follow your advice and will use a protection program.

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