Need some good advice

I have a plumber setting up an oxygen system for my ailing mom. Part of his bill of materials is an oxygen monitoring gauge with an audible and visual alarm. This is the gauge... http://pegasusalarmgauges.com/ ... it is the oxygen 1/4 inch one.

My question is:
Is this an industry standard for this type of plumbing? Or is this possibly a not needed extra?.... will a regular gauge without alarms suffice and be a little cheaper? Money is an issue... she/we are not rich.

thanks to anyone who takes the time to chime in on this.

Stephan...

will your mom die if the oxygen runs out?

different med gas codes for different areas
I do not know your area so i really can not answer if the low oxy sensor is required
seems your moms health must be pretty bad, for you not to be using a oxy concentrator