A broadcast of a signal is received at a first system from a second system at a first time. From the signal, a location of a target associated with the second system and a velocity of the target are determined relative to a location of the first system and a velocity of the first system. At the first system, using the location and the velocity of the first system and using the location and the velocity of the target, a likelihood is computed of a collision between the first system and the second system. A notification is sent from the first system about the likelihood of collision responsive to the likelihood of collision exceeding a threshold likelihood.