Many variants of this device are available. The approved ones (SCCA, et al) are reliable and yes, they're not "cheap" BUT: If you're looking to shut off power from the battery, and it's NOT a race-car, hide the thing up under the passenger footwell to inturrupt current to the solenoid from the battery. That's strictly for long storage issues. But if it's an anti-theft device:
With my street cars I tend to "hide it in plain sight." I just put a standard Lucas toggle switch in the dashboard "array" that MUST be "on" to operate the fuel pump. If it's not in the on position the car will travel a few yards, and then cut out... and I'll be umm...err... well, suffice it to say there'd be one STUNNED perp in the event of an attempted theft. The storage thing is simply a matter of disconnecting the battery.