system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do smelling salts wake you up after you’ve been unconscious?

Also as a side note, could you sniff them to keep you awake?
gpt
They release ammonia gas. Ammonia is an irritant that triggers an inhalation reflex, which also increases heart rate. This cancels the physical effects of fainting - a reduced heart rate, breathing and metabolism in general. 

It won't keep you awake, but it can keep you from passing out in certain situations.