The Cricket hardware has three LEDs, which you can use to infer a few things about the device's state. At startup, all the LEDs light up for 500 milliseconds. At run time the LEDs light up as shown in the following table:
| LED | Listener | Beacon |
| Green (D3) | lights up when a | lights up for 150 microseconds |
| valid RF chirp | during ultrasound trasmission | |
| arrives from a beacon | (may not be visible in bright light) | |
| Red (D2) | lights up when a | lights up for 150 microseconds, |
| collision occurs (e.g., due to hidden | when the beacon fails to | |
| terminal or improper beaconing) | grab a time slot to send a chirp | |
| Yellow (D4) | lights up when an | Not used yet |
| RF message is received | ||
| but with no ultrasonic pulse |