A device, method, and system are provided for monitoring the delivery of fluids through a drip chamber. The device includes an electromagnetic radiation (EMR) source and an EMR detector. A device body is employed to position the source and detector about the drip chamber so that the source and detector define an optical path across the drip chamber. A processor device is employed to detect fluid drops from differences between detector signal values separated by a lag time. The flow rate is determined from a drip factor and the detection of multiple drops. In the context of delivering intravenous (IV) fluids, a battery powered handheld monitoring device that includes the source, detector, device body, and processor device may be affixed to a drip chamber included in an infusion set. The device includes a user interface, including buttons, a display, and an audio speaker, for the input and output of information.