Paladin
Contributor
If you're using an unbalanced, downstream reg like an Aquarius connected to a Sherwood (or other make) J valve with an audible warning, you get a series of warnings: The reg starts to get more resistant to breathe through at about 750 PSI. At 500 PSI, the J valve starts to vibrate and makes the tank ring like a bell and gets louder with every breath. At 300 PSI, the J valve cuts off and you have to pull the reserve rod. After all this, if you're not well on your way back to the surface, then you probably deserve the consequences.