Even if people are in deep coma, people still breathe. This design helps people to send "help me" or "mayday" call continiously by breathing of hunan body.

即使人在昏迷状况下，呼吸活动也仍然在进行，这款呼救器的设计就是利用人的呼吸可以不间断地发出求救信号。

youdao

So I took off my shirt and wrapped it around my head to help me breathe and it worked, but my eyes were stinging real bad.

BBC: The survivors' stories