The finger through the hand RC has always failed me. The looking at the hand RC started failing me so I stopped doing it. The text RC has failed me once, but I don't regularly use it anyway. the pinch/bite your tongue RC I've only used as a secondary check, but it seems reliable as that. The nose RC has been my most reliable one. The first time I used it I blew out and it failed, but every time since then I have breathed in and it's worked.