Tube train fart alarm

I've noticed when travelling on the underground trains in London that often the smell of a fart is noticeable. There is very little way of determining who carried out the act of grunting which makes it difficult to convince people that it wasn't oneself who let out the tommy-squeaker. What I would suggest is a guff-activated alarm, built into the underwear, that screams out the name of the person who trumped. It wouldn't need to be a nasty message, simply a notice of air-passing such as 'Sorry, due to <reason>, I have inadvertently dropped one". This would avoid the embarrassment of taking blame for the air-biscuit that wasn't caused by oneself.