The RTL-SDR can be used to listen to these ADS-B (Automatic Dependent Surveillance-Broadcast) Mode-S transponder signals, which can then be used to create your very own home aircraft radar system.
rtl_adsb, a simple ADS-B decoder
Use: rtl_adsb [-R] [-g gain] [-p ppm] [output file]
[-d device_index (default: 0)]
[-V verbove output (default: off)]
[-S show short frames (default: off)]
[-Q quality (0: no sanity checks, 0.5: half bit, 1: one bit (default), 2: two bits)]
[-e allowed_errors (default: 5)]
[-g tuner_gain (default: automatic)]
[-p ppm_error (default: 0)]
filename (a '-' dumps samples to stdout)
(omitting the filename also uses stdout)
Streaming with netcat:
rtl_adsb | netcat -lp 8080
while true; do rtl_adsb | nc -lp 8080; done
Streaming with socat:
rtl_adsb | socat -u - TCP4:sdrsharp.com:47806