It is a difficult question but I think manageable if what is proposed is to record the location when a question is answered. Ie using the audit log. When they are answering questions then presumably the enumerator is working and if they answer that question in a bar then its not unreasonable for the employer to know. If they spend their time in the bar playing candy crush then no location will be recorded?
It would be good to have an icon at the top of the phones UI displayed to indicate that the GPS location is being recorded while the form is completed. I take it the GPS icon that Yaw refers to just indicates that GPS is enabled ? Could an ODK specific icon be added to show that it is also being recorded?