If you use homemade ring+contact sensors- they are cheap so use a number 
of them in different planes. Pick(PIC?) the one not shorted when arming.
D

> 
> but don't these suffer from the same problem as a mercury switch ? Say
> the cylinder is mounted horizontally in the veehickle. If it's then parked
> on an angle (hill, verge etc) the angle could be great enough for the weight
> of the ball to hold it steady and not respond to small tampering vibrations
> ?
> 
> A couple of other points - I've less than 3 weeks to get this marketable at
> a sale price of NZ$40-$50. Wish I had more time. Really wish I had more.
> Basically anything not OTS is out, the lead times are just too long
> 
> I'm wondering what I could do with something springy ............
> 

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