Telling which direction a siren is coming from is really, really easy. You can do it with three electret microphones and a $1 ARM chip. A simple TDOA multilater

Telling which direction a siren is coming from is really, really easy. You can do it with three electret microphones and a $1 ARM chip. A simple TDOA multilateration algorithm will do a far better job of it than a human, even in complex reverberant environments. Reliably understanding speech is effectively strong AI. Humans don't speak very clearly, but we're spectacularly good at inferring meaning from context. Accurate transcripts of colloquial speech are often completely incomprehensible, because a vast amount of information is conveyed through context. When we're listening to someone speak, we're decoding the phonemes into symbols, but we're also constructing a model of the speaker's mind and predicting what they mean to say.