In wireless sensor networks, a high level of accuracy is required in time synchronization to maintain time consistency of sensed data and to reduce idle listening times. In this technical note, we propose two fully distributed protocols for time synchronization. They are based on algorithms of multi-agent consensus and hence do not require any leader node. Further, they employ an event-based scheme to enhance communication efficiency. We analyze their convergence properties and show that clock synchronization can be achieved with less communication at guaranteed precision.