It is no hassle to replace your bad sensor(s) if the wiring is already there. No worry about positive or negative in these low-voltage currents. Just make sure your system is NC (normally closed) - which means the door or window contact and the magnet are side-by-side when the loop is closed. Separate them and you trigger the (fault) alarm.

At 2" long, these magnetic door/window sensors are a bit bigger than the micro switches I've been using as alarm contacts, but they seem to be well built, and as long as you are OK with the larger size, they should work well. The philips-head screw terminals are a bit rounded over for my tastes, but they still seem to function as expected. I do like having one oval mounting hole, which gives you some leeway in your initial measuring and drilling, too.

It would have helpful if an instruction sheet were included -- it is not completely clear how to safely open up the blocks or if the magnet needs to be mounted in a specific orientation -- but careful prying with a screwdriver opened them up just fine, and testing with my multimeter confirmed that the switches indeed triggered once the magnet got within about 1" in ANY orientation. As such, I suppose instructions might be unneeded -- but there was a white sheet of cardboard included, so that would be an ideal place to indicate this.

Worked perfectly

I had some remodeling work done on my house and a couple of the window sensors were removed and not replaced. I called my big blue alarm company and they wanted to charge a fee just to come out, then whatever they would charge for the sensors.
My alarm system didn't recognize the windows without the sensors, and therefore I felt that when I would try to set the alarm, my home wasn't quite secure enough.
These contacts saved me a bunch of money. I placed them on my windows and, voila!, my alarm system recognized them, and I am back up and running. I was initially skeptical, but am now a fan of these.
I do recommend the WESUA contacts.

As expected