Alarm Sound

Brother R and his friend M are working together at Sierra Lodge, and Brother M notices a faint sound of some kind of alarm going off. 

It was faint, but then the alarm sound started to get louder and louder... and then Brother R comes into the room, and says, "Do you hear that alarm sound?  I'm trying to figure out where it's coming from."

And then as Brother R leaves the room, the alarm sound got fainter again. 

Brother R, of course, had a hard time finding the source of that sound, because from his perspective, the volume of the alarm seemed constant, no matter where he went.  It was a few minutes before Brother R realized that the alarm sound was coming from his own cell phone.