In this paper we consider the design of MAC protocol for real-time sensor network applications. Although existing wakeup scheduling techniques suggest end-to-end delay guarantees for such applications, their fixed wakeup schedules may not meet such constraints when multiple sensors compete for the event delivery at the same time. We propose a new MAC protocol called SPEED-MAC that can provide real-time delay guarantees with much lower energy consumption for both single-source and multi-source events. The main ideas underlying the protocol are two-fold. First, we introduce a novel wakeup technique called signaling wakeup period, which is small enough to detect collisions and contentions. By employing the signaling wakeup we can minimize the event report latency as well as the idle listening. Second, to resolve the collisions and contentions incurred by multi-source events, the protocol employs adaptive wakeups that combines static scheduling with contention-based media access control depending on the type of traffic. Our simulation results show that SPEED-MAC can achieve an order of magnitude energy savings while providing near optimal latency compared to the existing solutions.