We used a randomized controlled trial to test the effect of mass deployment of TASERs on policing. The findings show that the presence of a TASER is causally linked to statistically significant increases in the use of force more generally—a 48% higher incidence during treatment conditions for TASER-equipped officers, a 19% higher incidence for non-TASER-equipped officers, and a 23% higher rate force wide, compared to control conditions. Assaults of officers doubled. However, there were fewer complaints during treatment compared to control conditions (five versus nine complaints). We conclude that, as is the case with other types of weapons, the presence of TASERs leads to increased aggression. The visual cue of a TASER in police–public interactions leads to aggression. Given other benefits of TASERs for policing identified by previous studies, our findings suggest that both enhanced training as well as concealment of TASERS should be considered.