An inexpensive and easy to build and deploy device to measure immersion times is described. The device consists of an LCD timer mounted in a small waterproof PVC housing. Time is recorded and integrated when seawater creates a connection between two stainless steel contacts. The device was tested in the laboratory and under field conditions on a wave swept shore. Under laboratory and field conditions, the device gave precise estimates of immersion times with maximum error of less than 4%. Applicability of this device in ecological and physiological studies is discussed and compared to other methods proposed in the literature.