Yes, I have returned the monoprice door contact. I ended up getting a zigbee one, Visonic MCT-340 E. So far much better. Smaller, connects really easy, has ability to have larger gap when I need for a few applications and finally, battery is good so far. Side benifit, has temperature reading as well. If this looks good in 1 month, I may look at getting more.
Not perfect for every situation, but 5v USB adapters for phones are really inexpensive and so are these step-down modules. As long as 800ma is enough. If not, there are other options with a higher output, for not much more.