It's not really about lying, IMO. (In any case, lying isn't even unethical. -- deceit is.) It's pretty much ok to deceive people if they indirectly agree to it

It's not really about lying, IMO. (In any case, lying isn't even unethical. -- deceit is.) It's pretty much ok to deceive people if they indirectly agree to it and you stay within bounds of what they agreed to. It is not unreasonable to expect people will be ok with deception conducted to engage in data collection and scientific study, so long as the consequences are negligible, as they are here. The only ethical problem here is caused if you do not use the collected data, or do not stop the study after a sufficient amount of data is collected.