This is the one I've fitted to my latest car.
The 'cut off fuel' bit of it isn't exactly a relay contact (if you were expecting continuity on the two wires then you'll be disappointed), instead it's more of a MOSFET circuit, ie it detects voltage on one side and replicates it on the other, until you send it a text and it stops outputting the voltage on the other side. I have it wired into my fuel pump feed.
It has a 5th wire which can be connected to a switched live (accessory) so it can send you a text if that wire goes live.
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