During California’s record-breaking September 2022 heat wave, the grid came within minutes of rolling blackouts, until an emergency text to 27 million phones asked residents to cut back. UC Davis researchers analyzed smart-thermostat data from more than 10,000 homes and found that air conditioning use kept climbing even at temperatures up to 110 °F, so today’s AC systems aren’t too small to keep up. But when they compared homes that got the emergency alert with similar homes that didn’t, AC use barely changed. The sudden drop in statewide demand that evening came from somewhere else, which makes it harder for grid planners to count on residential cooling cutbacks in the next, hotter heat wave.