While it is technically possible for an intruder to disable wireless entry sensors with an external magnet, it’s extremely unlikely.   It would require a very powerful, expensive magnet, and the intruder would need to know the exact location of the sensor on the inside of the door.  In order to know this, the person would have had to be inside your home previously.   Guessing the location wouldn’t disable it as the reed switches involved in the alarm process are very sensitive.  Trying to disable the alarm would be more likely to trip it than to render it dysfunctional.