This paper provides an alternative causal mechanism to explain why parties monitor voters. The ability to monitor voters, defined as a clientelistic party’s capacity to convince voters that it can identify the candidate(s) for whom they voted, remains a core assumption in the literature. The underlying logic of the argument is that if clientelistic parties cannot monitor voters, they run the risk of voters taking the goods with one hand and voting with the other. Instead of focusing on commitment, I argue that monitoring makes clientelism work by forcing voters to publicly signal their electoral support before getting to the voting booth. Using empirical evidence from Argentina, this article shows how parties mobilize and monitor voters before elections to avoid the costs of verifying their electoral choices on an individual basis.