Do you know of a exercise heart rate monitor that will beep or vibrate when my heart rate exceeds a certain level?

I’d like to get an app for my Apple Watch that would notify me immediately when my exercising heart rate goes above a 90% effort (140 bpm for my 70 year old heart).

Can’t get the “Workout” or “Cardiogram” apps on the Apple Watch to notify me when my heart rate goes too high.

I’ve been using “Polar Beat with blue tooth” with “Heart Watch” app that’s good at letting me know when my heart rate reaches 105 bpm (70% effort) by stating “improving fitness”. But I need notification when I exercise very hard at over 90% effort. I can’t divert my attention to look at a cell phone screen while exercising (also sun glare is an issue).

I tend to push too hard into my heart’s red zone (over 152 bpm or 100% effort). That’s not good. No more than 90% effort is what I want.