Crowd density monitoring is crucial to many applications, such as guiding tour and crowd control in commercial environments. Video or image-based solutions are high cost and cannot be applied in low-light environments. For some Radio Frequency (RF) based technologies, some people have to carry certain wireless transceivers, others also need to collect abundant fingerprint. These approaches are high cost and impractical. In this paper, we propose a crowd monitoring approach using mobile phone. Our design of crowd detection adopts clustering methods. Feature sets derive from Wi-Fi signal strength measurements. We use Bluetooth readings analyzing to estimate crowd density. We implement our design on off-the- shelf smartphones and evaluate its performance via extensive experiments in typical realworld scenes. Results of experiment verify the feasibility and the effectiveness of our proposed approach.