If there is a loss of/lack of air pressure at high altitude, without an explosive decompression (for instance as on Helios 522 or N47BA) are there any signs that pilots can look out for that they might not be getting enough oxygen?
Does an audible alarm exist on any commercial jets when cabin pressure is at a dangerous level?
It's my understanding that the brain is impaired, and reaction times are increased with oxygen deprivation. Are there any techniques to combat this, after noticing hypoxia onset? e.g. slowed breathing