Firewire Ni has been working hard on a device that will secure your Fuel tank. The device is called oilert and was released in august 2009....
Oilert is an electronic oil tank security device suitable for all sizes and shapes of oil tanks. This is a customised security device and works great with existing security systems.
The concept is very simple...
-The sensor on the oil tank (which is wireless) works on its own battery supply and sends signals to the receiver in the house
-Receiver in the house can be connected to your intruder alarm, telephone line or any other applicable device
-Only when the sender recognises a sharp fall in the drop of oil does it transmit an alarm to the receiver.
The system can also be used on any other liquid that you may want to secure.