We characterize the detection probability of blockage sensing by radars deployed on towers in cellular networks. If the signal-to-interference ratio of the reflected pilot signal is larger than the predefined threshold and there is no other blockage between the radar and the corresponding blockage, the radar successfully detects the blockage. Modeling radar and blockage locations using stochastic geometry, we derive the detection probability as a function of the system parameters, chiefly the radar and blockage densities. Leveraging the obtained expression, we provide some guidelines for efficiently deploying radars to enhance the detection probability.