Paramedics and EMTs!
Here's a simple little program that allows you to specify oxygen cylinder size, tank pressure, and flow rate to calculate how long the tank will last. There's a "set alarm" button which allows you to exit the application and do other things, then receive a reminder.
Quick Pick option for nasal cannula, face mask, and non-rebreather, or override with your own LPM specification. Also allows you to enter vent settings including tidal volume and FiO2%.
Full explanation, including formulas and limitations, in the program help (Menu -> Help).
Completely free, and ad-free.
V 1.2 disables the automatic deduction of a 500 PSI reserve if you manually enter a PSI less than 500. Alarm activation is changed to alarm when: Reserve is reached (if a reserve exists), or when tank becomes empty. Custom tank size supported.
V 1.1 changes the interface, restructures the display to hopefully accommodate more devices, and allows alarm cancellation as a separate feature.