David uses this device when Shaw begins to double over from the pain of the alien growing in her womb. It is a palm-sized cylinder with a large needle sticking out one end and a yellow button on the other. To administer it, he jams it into her shoulder, depressing the yellow button with his thumb, and holds it there until the spraying sound coming from it ceases.
This is not a hypospray (as described in Chapter 12, Medicine, of the book), which would not have a needle, so where is the sound coming from? It might be an audio augmentation to let the administrator know. This would be a reasonable sound, as it gives sense of pressure releasing. But there should be some clear signal—like a soft double-beep—when the doseage is complete, less it be removed too soon for misinterpreting the audio signal.