They use an algorithm to analyze the readings from the multiple sensor plates for a quicker, more accurate indication.
ðeɪ jˈuːz ɐn ˈælɡɚɹˌɪθəm tʊ ˈænɐlˌaɪz ðə ɹˈiːdɪŋz fɹʌmðə mˌʌltɪpəl sˈɛnsɚ plˈeɪts fɚɹə kwˈɪkɚ, mˈoːɹ ˈækjʊɹət ˌɪndɪkˈeɪʃən.