Some television companies in the US are trying to use controversial subliminal adverts, but they cannot hide from the system patented by Ericsson of Stockholm. By measuring the energy distribution in the video signal, Ericssons's system can detect the large changes that indicate a context change. If the detector spots two context changes in a split second, it sounds the alarm. Innocent context changes between close-ups and landscapes do not set off the alarm as the scene does not change again immidiately. TVs fitted with memory chips can capture the flash frame, allowing the offending advertiser to be identified.