We present Avrora, a cycle-accurate instruction-level sensor network simulator. Avrora scales to networks of up to 10,000 nodes and performs as much as 20 times faster than previous simulators with equivalent accuracy, handling as many as 25 nodes in real-time. Avrora emulates sensor nodes based on the Mica2 hardware platform, including the AVR microcontroller, its internal devices such as timers and serial port connections, and external devices such as the CC1000 radio. Avrora provides a platform for simulating, analyzing, and debugging sensor network programs in precise detail.