Unfortunately not. The major difference between an honest bot and a regular user is a single text string (the user agent). There’s no reason that bots have to be honest though and anyone can modify their user agent. You can go further and use something like Selenium to make your bot appear even more like a regular user including random human-like mouse movements. There are also a plethora of tools to fool captchas now too. It’s getting harder by the day to differentiate.
It’s more than you think. I work with the MSP430 microcontroller, which is capable of a sleep current of 40nA @ 2V, full active mode at 140uA/MHz with all onboard peripherals turned on. With this you could achieve almost a 20% on-off ratio with a 1MHz clock, or keep it in active mode all the time at ~150kHz, which is sufficient for many embedded sensor applications.