This neatly demonstrates the difference in diving of a lot of us.Chuckles .... my Peregrine does not beep, thank god, but the vibration alert on it is quite nice. I have 2 alerts set on mine, 85' and 3 min to NDL. One alert to remind me to slow down my descent, reaching my depth limit; and one alert to remind me it is time to start thinking about coming up.
The bottom is where you can't go deeper and varies with the target wreck. 40m/130ft, 50m/165ft, 60m/200ft, etc.. NDL's are meaningless as it's the TTS which you have to be on top of and it will vary according to conditions and when you've told the skipper you'll be back up...
The Petrel/Perdix/Nerd will alert you when the CNS has exceeded 100%, but that's just a message. If your PPO2 is high or low, you should be on to that. However it's possible if when ascending you mistime an oxygen injection it'll momentarily spike until it's pumped around the loop. Really don't want more bells and whistles going off as I know it's an issue.
Horses for courses.