Just added a couple quarters at a time until it… ahem… reached the tipping point.
No need for the magnet part of the sensor.
I’m going to try a less pricey Monoprice tilt detector (garage door sensor), but they are pretty big and in the wrong orientation to place on the door portion of the trap… ie, the part that falls closed.
Alas, I’ve not put these on all my Tilt Traps and had 1 mouse expire due to my negligence. 
Haha, that poor mouse. If you charge the mice rent, you may recoup the cost of outfitting additional traps. I may try using rocks in to tape down, then fine tune with pebbles or quarters.
It seems like you could use a cheaper door/window sensor and put the magnet down on the side of the body. So it would be in open all the time until the mouse comes to dine.
As far as how many quarters, it sounds like you added them based on feel, where it felt as sensitive as it was before you attached hardware — is that correct?
Yup.
We have very tiny mice (if any left?), and so the trap needs to be very sensitive to any change in balance. Won’t work well on a floor that gets a lot of vibrations from normal use.
What do you guys do with the trapped mouse (dumb question, I know ;))?
Take them out to a field and let them go. Try to get them out of neighborhoods. Where I am at there are plenty of wooded areas nearby. I had a mouse problem a few years back, always took them to the same spot.
I figure once I let them go its up to nature to decide.
Those tilt traps work great. I still set up traps every couple months, just to make sure I don’t have any guests. Also don’t have anything they may like easily accessible (ie in the garage, like birdseed)