Generally, collisions between packets are undesired in wireless networks. We design this scheme, Cooperative Jamming in Wireless Networks (CJWN), to make use of collision to protect secret DATA packets from being sniffed by a nearby eavesdropper. We are intending to greatly increase the Packet Error Rate (PER) at the eavesdropper when the PER at the receiver is maintained at an acceptable level. This scheme is not intended to completely take the place of various encryption/decryption schemes which are working based on successfully received packets. Adding CJWN to the popular CSMA/CA adopted in IEEE 802.11 will add more security even the key for encryption/decryption is already exposed. Because the overhead of CJWN is very big, we do not suggest using it on every transmission. When some secret packets have a high requirement of confidentiality, CJWN is worth trying at the cost of throughput performance and power.