@OutdoorMan this would be a workaround, but not a real solution. I would like to see an alarm that sounds a sound and vibrates to draw your attention to the fact that you reached (or exceeded) a target HR. I know that some of us want to reach a certain target zone when exercising, but some (other) of us need to watch the max HR (I don’t want to have a cardiac arrest when I am climbing ambitiously a hill on my bike ).
Btw. it is available on many bike computers. On my Garmin Edge, the alarm will sound, but it is hardly noticeable (and the text does not even change colour). I am afraid that it is designed as an alert for reaching a target zone (as opposed to a real “ALARM” (“slow down or you will die” type).