Is this a door opening alarm or is it a proximities alarm that sense only if the door is opened?

Hello Valued Customer, thank you for the question. This device sets off an alarm when the two magnets are separated. If you have any further questions or concerns, please feel free to give us a call between the hours of 7 AM – 8 PM Central Standard Time, Monday thru Friday at 1-800-654-8483, press option 4, and provide our Consumer Care Team with your personal ticket number 520028, so that we can resolve your issue promptly.