Organic electrochemical transistors (OECTs) allow current to flow in devices like implantable biosensors. But scientists long knew about a quirk of OECTs that no one could explain: When an OECT is switched on, there is a lag before current reaches the desired operational level. When switched off, there is no lag. Current drops immediately. Researchers report that they have discovered the reason for this activation lag, and in the process are paving the way to custom-tailored OECTs for a growing list of applications in biosensing, brain-inspired computation and beyond.