Behavioral studies often aim to perform specific actions on focal individuals and could benefit from automated procedures. With this paper, our goal is to demonstrate to ecologists that building a selective, automated device triggered by radio frequency identification detection (RFID) running on a battery is easy and affordable (similar to 100 Euros). We provide a step-by-step description of how to build such an RFID triggered trap for small animals. We built and tested our selective traps in a colony of 300 captive bats, flying in a 40-m-diameter dome. Our device proved successful in trapping focal individuals using RFID identification while recording every single visit to the trap-feeder. Our guide not only provides information for building RFID-triggered traps, but also offers a general framework for building any device triggered by RFID and can thus help build tailored setups matching specific studies requirement. Home-made selective device using RFID detection have a great potential in opening-up exciting new possibilities for a wide range of studies on animals, ranging from trapping specific individuals, to automatically monitoring activities at the nest-box, or supplementing specific individuals in a population.