Wireless Sensor Networks (WSN) consist of devices with limited resources to explore and sense the environment in a cooperative way. Security, mainly in terms of guaranteeing the data integrity, is a primary issue for many applications, but with an extra energy cost. Thus, trade-off is required between security level and energy consumption in real applications. First of all, a brief survey about security methods, focusing in data integrity, in WSN is implemented. The objective of this paper is to propose a new data integrity method with medium security levels and low energy cost. Therefore, we propose a new and lightweight mechanism for data integrity with overlapping blocks in WSNs. Hence, an attacker will spend much time and effort to interpret and alter the packets. The experiments were performed using TinyOS 2.1 operating system and TelosB nodes for measuring the overhead in terms of energy consumption, memory, and packet size. Moreover, the receiver is able to detect tampering packets and request those retransmission data. An attacker would require huge amounts of memory and processing time to extract the original information, even for small-sized data blocks. Thus, this fact makes this approach a simple, yet effective, mechanism to protect data whilst enhancing the data integrity.