I've had 2 hoses at the back of the engine fail, one of which lead to HGF, it happened on a motorway and I only realised when I pulled off and was enveloped in steam. The hose that failed in both cases was PEH100940, it's quite close to the exhaust and has got a joint in it. Because of this I always fit a low coolant alarm to my cars.
My latest car is an F Steptronic, I wasn't sure how long I'd be keeping it so I developed an easy fit alarm. It uses a tank as fitted to 2005 cars and all the electronics including LED and warning buzzer are fitted in a switch blank.
If anyones interested I made a short(ish) video showing it.
Interesting video. I would be interested which timer/processor you used for this purpose?
What I used is led and buzzer which is control with relay with timer for 10 sec delay, so no three marktimes and no ignition switch contact check.