Museo Nacional de Ciencias Naturales 1 article published in JoVE Environment BtM, a Low-cost Open-source Datalogger to Estimate the Water Content of Nonvascular Cryptogams María Leo*1, Angel Lareo*2, Carlos Garcia-Saura2, Joaquín Hortal3,4, Nagore G. Medina5 1Real Jardín Botánico (CSIC-RJB), 2Grupo de Neurocomputación Biológica, Dpto. de Ingeniería Informática, Escuela Politécnica Superior, Universidad Autónoma de Madrid, 3Department of Biogeography and Global Change, Museo Nacional de Ciencias Naturales (MNCN-CSIC), 4Centre for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências da Universidade de Lisboa, 5Department of Botany, Faculty of Science, University of South Bohemia We present a simple and cost-effective method to build an open-source datalogger that measures the conductance of nonvascular cryptogams together with the environmental temperature and humidity. We describe the hardware design of the datalogger and provide step-by-step assembly instructions, the list of required open-source logging software, the code to run the datalogger, and a calibration protocol.