FlightSafety had a hypoxia simulation program that ended a couple of years ago. The device was hooked up in the simulator and regulated the O2/N ratio. It was developed in concert with the Mayo clinic. It got good reviews and positive results. The difference - between this and the altitude chamber - was that you could see how it impacted your ability to comply with a clearance, fly, etc.

On one simulator session a reporter occupied the seat and alleged that he had a medical emergency using the equipment. The instructor was about to call 911 and get the defibrillator when he suddenly "came to" and self proclaimed he was well.

The implication was that he feigned the illness to get an angle on a story. Regardless, FSI terminated the program thereafter.

I never had a chance to use it but I did do through the altitude chamber at Wright-Patterson AFB circa 1993. Invaluable experience.