A low cost, stand-alone RF power monitor was developed that fulfills the requirements given in the standard 60601-2-33 and is based on electrical standard components. It consists of two dual directional couplers, two RMS envelope filters and a microcontroller. A fixed power limit can be programmed or patient dependent power limits can be communicated from a host computer. Evaluation measurements show power measurement and RFPA blanking switching times accuracies with an error less than 1%. A sampling rate of 130kSamples/s indicates usability for relatively short or moderate complex shaped RF waveforms.