Compact, chip-based lasers have conquered much of the electromagnetic spectrum, from ultraviolet to infrared, enabling technologies from digital communications and barcode readers to laser pointers and printers. But one key region of the spectrum remained untamed: the terahertz band, which lies between infrared light and microwaves. Engineers hankered for a ready source of terahertz radiation, which can penetrate opaque objects and probe chemical fingerprints inside. But compact terahertz lasers have only worked at ultralow temperatures, limiting them mostly to laboratory settings.