A cluster turns electricity into heat at close to 100% efficiency, and both ends of that conversion are measurable from outside: the power has to come from somewhere, and the heat has to go somewhere. Measurement and signature intelligence (MASINT) reads those two quantities and estimates how much compute is running here.
Heat
Almost all the electricity a data centre consumes ends up as heat. A large training run can keep chips under a fairly constant load for weeks, so the cooling system has to remove roughly the same amount of heat, day and night. Inference often varies with user demand. A sustained thermal signature can therefore be evidence of continuous, intensive use—not just that a site has the capacity for it. However it is important to note that a Prover may disguise energy consumption as other high-energy activities and obtaining detailed energy consumption data can be hard.
Read the release.
SatVu (2025) | 3 min
Commercial thermal satellites such as HotSat can resolve individual buildings. SatVu has published thermal imagery of an operating US data centre showing which cooling equipment, substations and electrical yards appear active. There are simpler indicators too: Baker et al. note that roofs where snow does not settle in winter can reveal waste heat (footnote 127). That may be visible in ordinary optical satellite imagery, without a thermal sensor.
But heat does not tell us what the chips are doing. It provides evidence of activity and a rough indication of its scale, not a reliable distinction between training and inference. A Prover could run inference between training runs to keep power consumption—and heat output—roughly constant. The workload would change; the thermal signature would not necessarily show it.
Verification Methods for International AI Agreements
Read the "Energy monitoring" entry under national technical means: the description, the historical precedents, and the evasion techniques. Note what they mean by "coarse": the method can catch a facility drawing far more than it declares, and cannot catch a run that fits inside an authorised facility's normal draw. The evasion list is the one to keep.
Wasil, Reed, Miller, and Barnett | arXiv (2024) | 5 min
Optional: Mechanisms to Verify International Agreements About AI Development
Read the national-intelligence building blocks and the locating-compute appendix (pp. 67–80), the source of the feasibility ratings quoted in the module and of the feasibility cards in 2.3.6.
Scher and Thiergart | MIRI (2024) | 30 min
Optional: xAI is facing a lawsuit for operating over 400 MW of gas turbines without permits
How the Memphis case was established: aerial photographs commissioned by the Southern Environmental Law Center in March 2025 showed 35 turbines around the Colossus site; thermal images about a month later showed at least 33 of them running; a June flight counted 26. The permit issued in July 2025 allows 15 generators, 247 MW.
Tim De Chant | TechCrunch (2025) | 5 min
Interactive: The Power Signature
The explainer below is built from Epoch's datacenter dataset. It places a real facility beside national grids for scale, shows which features of its load a watcher can and cannot read, and projects how fast the signature shrinks as performance per watt improves.