Actually the fact the the users don't pay for it is not relevant. You're still making a transaction with the user, providing them with a service, in exchange for them putting up with your ads. But in reality the service you say you're providing is false.
The extent of the technological capabilities of a device like a smartphone are far from common knowledge for the typical user. An app can allow your phone to perform the functions of a gps, why can't it allow your phone to perform the functions of a radar detector? I mean even people who know enough about their devices to know that the idea of it acting as a radar detector is unreasonable may not know what their phone IS capable of. How more technologically proficient users do you suppose are there who are completely unaware of the fact that their phone might have a barometer?
