> Do you seriously think that if Google sees the same hardware identifier 1000s of times a day they are not going to consider that usage to be fraud?

Phones are very cheap, especially refurbished phones. Just have the phones mimic real life sleep/wake cycles and take occasional breaks. Use 25% more devices to account for the loss in uptime.

Besides, some people (often unemployed or disabled, and possibly with sleep disorders or mania) actually don’t do anything other than scroll on their phone all day and night. So you can’t rely on this as a good signal without creating even more blowback. And you really don’t want too much blowback from troubled people who have infinite free time.