This a Motorola/Freescale relative pressure sensor, intended for medical applications. The chip measures the pressure difference between the front (chip die visible) and the back (white side). The back side has a dab of black silicone gel that protects the die against the gas or fluid of which pressure is measured. This sensor has a customer part number, but it is similar to the MPX2300DT1.
As a simple test, I connected 5V to the Gnd and Vs leads, and measured the voltage between S- and S+ with a multimeter. Left alone the multimeter reads 0.0 mV. When I put a straw around the gel hole and blow in the straw the multimeter reads 0.9 mV. This looks like a good sensor for a suck and blow (sip and puf?) switch.
Using this sensor as an absolute sensor (to measure atmospheric pressure) might be possible, but you must seal either the front (gel side) or the back (open chip die) side. I do not know whether this is realistic. Let me know if you succeed in doing this!
This is a surplus product. It was obtained from a surplus store, from an inventory or from any other secondary source. You can expect this product to be in good working condition, but it can show signs of being handled, shipped, repackaged etc. The supply of a surplus article can suddenly run out, or the price can change. Get it while it is available.