Fuel Drop or increase Alert

Lets suppose i have an attribute that shows the lt's a car has in its tank.
How can i issue an alert when someone lets say stole gas (dropfuel >xx lt's from previous measurement )
or put gas (increase lt >xx from previous measurement) on the tank.
Thanks

For fuel drop there is already a special alert available. You just need to configure the drop threshold in device attributes.

Hi can you tell me where i can't find it.