In this paper, we have proposed a current-bypass anti-tampering algorithm for single-phase and three-phase smart meters by using a single chip solution from Analog Devices together with the proper threshold of the unbalance current difference between phase and neutral lines. Essentially, the current bypass anti-tampering algorithm is implemented to help the smart meter overcoming the tampering events of bypassing the main line and load line for both single-phase and three-phase power systems. Practically experimental results show that the proposed algorithm offers a wide dynamic range of tampering event detection, a low-probability of false detection, and a fast speed of tampering detection. Furthermore, in the case of small energy measurement, the proposed algorithm still yields a precise and accurate tampering detection capability, making it suitable for real application.