Abstract Surface pressure impulse propagation through a monolayer at the air-water interface has been investigated. The pressure impulse confined to the monolayer plane is produced by the photoisomerization of an amphiphilic spiropyran. Arachidic acid, dimyristoylphosphatidylcholine and monomethyloctadecanedioate have been used as transmitting layers. The pressure impulse is detected with a microphone-type sensor at various distances. The longitudinal pulse velocity is in the 50–260 cm s −1 range. The results are interpreted in terms of a simple model in which a thin water layer under the monolayer moves along with it. The thickness of this layer is estimated to be about 100 μm, independent of the transmitting layer. It is also concluded that the dynamical compression modulus is up to four times larger than the stationary compression modulus.