Lots of consumer products have a pressure transducer. Justine got a Tissot Touch watch c. 2003 which had an “altimeter”. Not much else on that watch worked 
Obviously there is no (practically accessible) QNH subscale… but while I don’t know the dynamic pressure component of the total pressure measured by a pitot tube, it is probably measurable easily enough.
UdoR wrote:
Just an assumption: some smartphones like the iPhone have barometric sensors. This might be used?
That’s already what they are using. They would obviously get a relative reading wrt no velocity at that point in time. Doing this every day, and the relative readings will be fairly similar for all days. The gradient would be fine, but the zero point will not. Think of it as ASI = a*pressure + b. You will get the “a” but not the “b”. In an aircraft you wouldn’t be able to tell if the velocity was increasing or the altitude was decreasing 
To get the velocity you will need total and static pressure. The speed is a function of P_total – P_static, and you need to measure both. I took off with the static port blocked once. What happened was everything looked OK until the aircraft started to gain altitude. Then the ASI wandered all over the place in random fashion. Theoretically the ASI should probably show way too low speed, but I guess it wasn’t completely blocked.
