It's no surprise that people are more honest when they know that they're being watched. But what about just reminding them of the idea of being watched, without them actually being watched?
For years, people at the University of Newcastle's Division of Psychology have an honor (or trust) system where they are requested to deposit payment for coffee in an "honesty box." There was a note saying how much they should pay.
In 2006, Melissa Bateson and colleagues decided to do a little experiment: they placed an image above the note. They alternate between two pictures: one week they would use a picture of eyes and the other week, flowers.
After 10 weeks, they plotted the amount of money received versus drinks consumed and found that people paid nearly three times as much for their drinks when eyes were displayed!