With the maturity of 5G networks and V2X technologies, utilizing V2X to increase driving safety becomes feasible. Road side units (RSU) recognize dangerous events and notify the related vehicles using 5G V2X communications. The alert latency between RSUs and related vehicles may cause car accidents. Besides, the V2X emergency alarms are broadcasted by dipole antennas. Many unrelated vehicles will receive unnecessary alerts and distract drivers. This paper proposes an accurate vehicle-to-vehicle instant alert system (V2V-IAS) to detect potential dangerous events and alert target vehicles by directional antennas to reduce transmission delay and interference. In V2V-IAS, a vehicle can fuse camera information and cooperative awareness messages (CAM) messages from surrounding vehicles carried to predict dangerous events without relying on RSUs. Once an event is detected, the vehicle will send an alert to specific cars in real time using directional antennas to increase the transmission success rate and reduce disturbing unrelated vehicles. We also use two sets of Qualcomm MDM9150 to conduct real road tests and simulate multi-vehicle environments on Matlab to validate our idea. From experiments, directional antennas can reduce the possibility of packet collisions up to 21% and transmit at the same distance with less output power compared to dipole antennas.