coil if undamped can produce 1000's of volts...the circuits on the sensing end can be destroyed if they're not properly designed to handle such events.

The diode will fix this for you...it will slightly slow the opening of the relay...but in the context of this application you could care less.

I'd put those diodes on ASAP :-) Cathode end towards the postive supply...Anode end towards the negative supply...then you're golden.

Regards,

James R.