Using a non-invasive charge detection method, we detect a flow of electrons trapped in dynamic quantum dots. The dynamic quantum dots are defined by surface acoustic waves (SAWs) and move through a long depleted one-dimensional channel. A one-dimensional constriction is placed next to the SAW channel but in a separate circuit; the current induced by the SAWs through this detector constriction is sensitive to the number of electrons trapped in the SAW minima. We observe steps in the detector acoustoelectric current as the number of electrons carried by SAWs are varied as 1, 2, 3....