> Except for one person with a blocked nose, all woke up within two minutes of the smell reaching them.

Seems like a pretty bad failure mode, if it doesn’t work when people have a bad cold.

Also, the time delay is an issue. An audible alarm can wake people up much faster.

One thing they might be to use an sound based alarm, but that has enough low frequencies that it makes your skull resonate. A lot of dead people, may have conduction issues, and the sound can be transmitted through bone. For the people that have a neurological basis for deafness, even sounds that you cannot perceive if they resonate the right structures can make you feel uncomfortable.