Sleeping heart rate typically below 40 bpm

Is the a way to set the alarm for low heart rate to 35 bpm? I am healthy and active, but have a low heart rate when I sleep (typically 37-42 bpm). I have been thoroughly checked by a cardiologist. He said it’s not unusual for athletic people to have sleeping heart rates below 40 bpm. I’d like to use the alarm to monitor my heart rate but the lowest it goes is 40 bpm. I’m going to have to turn it off so I can sleep.