No, the backdoor can use some activation mechanism on chip to avoid drawing power when not in use, then the additional power draw will be so low that it's essen

No, the backdoor can use some activation mechanism on chip to avoid drawing power when not in use, then the additional power draw will be so low that it's essentially undetectable. Tbh you'd have a hard time since either you're trying to measure a few milliwatts in a very noisy environment (either very low wattage, so various effects dominate, or high wattage, where your equipment will quickly get very very expensive).