Most social-science studies are designed to elicit answers in such a way that the participant doesn't realize what question is actually being asked. For example, when William Labov studied the distribution of rhoticity in spoken English, he asked people innocuous questions whose answers contained the sound /r/ in (phonetic) environments where rhoticity can occur. He'd go into a multi-story department store, look at the map, and ask an employee something along the lines of "Where can I find towels?" so that the person would answer "Those are on the fourth floor." Similarly, the wi-fi study wasn't looking at usability any more than Labov was interested in towels; they were really eliciting "willingness to do something dangerous" as a proxy for (lack of) risk awareness. As long as the measure is wearing unique clothing, participants shouldn't be able to recognize it.