One of the extensively studied coverage models in wireless sensor networks is barrier coverage, which guarantees that any movement crossing the given belt must be detected, while the direction of the movement is not required. For some intrusion detection applications, it may be the case that only one direction of crossing (the belt) is illegal such as border guarding. Therefore, we introduce a new coverage model called one-way barrier coverage, which requires that the network reports illegal intruders while ignores legal intruders. We propose an appropriate definition for one-way barrier coverage. We deeply investigate one-way barrier coverage with binary sensors. Our research illustrates that it is not straightforward to provide oneway barrier coverage even though there is only one intruder. When there are multiple intruders, we introduce the concept of neighboring barriers and design different protocols to provide one-way barrier coverage for different sensor models based on neighboring barriers.