Increasing numbers of studies are recording detailed temperature data for characterization of ground water–stream exchange. We examined laboratory and field operation of a small-diameter, stand-alone and inexpensive temperature logger capable of investigating stream–ground water exchange was examined. The Thermochron iButton is a 17.35-mm-diameter by 6-mm-thick instrument that costs <$10 when ordered in quantity. Testing of the loggers in a controlled temperature bath revealed a precision of ±0.4°C and an accuracy of ±0.5°C for a group of 201. More than 500 loggers have been installed in channels and in subchannel and floodplain ground water environments in two gravel-bedded rivers in the western United States. Loggers were placed as single devices and in vertical arrays in monitoring wells with diameters of 10.16, 5.08, 2.54, and 1.9 cm. We determined that the loggers have four principal advantages over more commonly used wired and currently available stand-alone logging devices: (1) the wireless nature does not require the instrument location to be associated with a control-recording system; (2) the small size allows for installation in small hand-driven or direct-push monitoring wells and thus intimate contact of the instruments with the hydrologic environment; (3) multiple loggers are easily suspended in a single fully perforated monitoring well, allowing for the collection of high-resolution temperature profile data; and (4) the low cost of the loggers allows for the deployment of large numbers, thus improving spatial resolution in shallow ground water floodplain scale studies.