Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 5_0_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A405 Safari/7534.48.3)
Then no. I use Siri in my car all the time and with all the road noise, wind noise etc there's no chance of Siri hearing you on your lap.