[Yes, I searched.]
I'm looking for a basic HRM that beeps when I'm IN target zone, not out of it. Cheap is good, too.
The only ones I've found are the Sports Instruments HRMs, alas from a defunct business and increasingly difficult to find still operating. The good news is that when you find 'em, they're cheap. . .lots of clever features, too.
Anyway, I'd rather hear the beep when I've 'climbed' into Zones 4 or 5 rather than listen to it nag me endlessly during warm-up or between sets. Make sense?