State-of-the-art sensors use active electronics to detect and discriminate light(1-3), sound(4,5), vibration(6,7) and other signals(8,9). They consume power constantly, even when there is no relevant data to be detected, which limits their lifetime and results in high costs of deployment and maintenance for unattended sensor networks. Here we propose a device concept that fundamentally breaks this paradigm-the sensors remain dormant with near-zero power consumption until awakened by a specific physical signature associated with an event of interest. In particular, we demonstrate infrared digitizing sensors that consist of plasmonically enhanced micromechanical photoswitches (PMPs) that selectively harvest the impinging electromagnetic energy in design-defined spectral bands of interest, and use it to create mechanically a conducting channel between two electrical contacts, without the need for any additional power source. Our zero-power digitizing sensor prototypes produce a digitized output bit (that is, a large and sharp off-to-on state transition with an on/off conductance ratio >10(12) and subthreshold slope >9 dec nW(-1)) when exposed to infrared radiation in a specific narrow spectral band (similar to 900 nm bandwidth in the mid-infrared) with the intensity above a power threshold of only similar to 500 nW, which is not achievable with any existing photoswitch technologies.