Not familiar with 737, but some alpha sensors look at first sight like a metal cylinder sticking out of the side of the fuselage, about 2 inches long and a quarter inch diameter. They have no wing-like surfaces on them and it is not immediately obvious how they align themselves with the flow. In fact they have a slit along one side. This connects to a circular chamber inside the fuselage skin which has a vane in it and the external cylinder moves until pressure is equalised either side of this vane. Easier to de-ice, less drag, less vulnerable to birdstrikes than an external vane. These vanes always over-read because of the local flow round the fuselage, but this is normally taken out in converting the signal to the display so that the alpha gauge normally reads in units that are something like degrees of incidence. It is normal to have a sensor each side of the fuselage to take out the effects of sideslip.