Some of the aircraft available on FlightAware or FlightRadar24 around the United States for Aircraft Tracking or Flight tracking.
Reach Air Medical Services in California area.
http://flightaware.com/live/flight/REH1
http://flightaware.com/live/flight/REH3
http://flightaware.com/live/flight/REH7
http://flightaware.com/live/flight/REH9
http://flightaware.com/live/flight/REH11
http://flightaware.com/live/flight/REH13
etc...
Mercy Life Line Air Medical Service - Missouri state area.
http://flightaware.com/live/flight/N526T
http://flightaware.com/live/flight/N156V
http://flightaware.com/live/flight/N335ML
&
County Of Tulare Sheriffs Office - California
Aircraft: Flight Design GMBH CTLS (FDCT) (small plane) - (Equipped with ADS-B)
http://www.flightradar24.com/data/airplanes/N911TS
County Of Fairfax, Virginia
Aircraft: Bell 429 (B407) - (Equipped with ADS-B)
http://www.flightradar24.com/data/airplanes/N211FX
http://www.flightradar24.com/data/airplanes/N212FX
City Of Ontario, California
Aircraft: Eurocopter As.350B2 (AS50) - (Equipped with ADS-B)
http://www.flightradar24.com/data/airplanes/N50NT
N136MH - MedSTAR helicopter in Maryland.
Aircraft: Eurocopter EC135-T1 (EC35) - (Equipped with ADS-B)
http://www.flightradar24.com/data/airplanes/n136mh
Southern California List - Mostly with Mode-S only:
Air Medical Ambulance Aircraft Fleet in California
http://www.scanriverside.com/forums/...php?f=46&t=496
Southern California Police/Sheriff Department Aircraft Fleet
http://www.scanriverside.com/forums/...php?f=46&t=434
Some of the News Media helicopter around the countries(United States,Canada,UK,etc) equipped with Mode-S only and some don't have Mode-S yet.
If it's equipped with Mode-S you can use aircraft tracking software/Mode-S box to alert you via email text each time the Police/Fire/Medical aircraft gets in the air.
If the aircraft equipped with ADS-B and in coverage area on sites like FlightRadar24/PlaneFinder,etc.
You can use their Smartphone/Tablet/Computer Apps to alert you each time it's flying.
If the area isn't covered with ADS-B coverage. You can request free box kits from FlightRadar24 or PlaneFinder.
http://www.flightradar24.com/free-ads-b-equipment (Doesn't need a PC to run, Just plug the Ethernet & Antenna cables into the box to upload from your area)
http://planefinder.net/about/coverage/ - PlaneFinder has free boxes available. but it's required to use your personal computer.
The next step will be to MLAT aircraft via the transponder signal. FlightRadar24 will be releasing MLAT viewing later in February or March.
Info on how MLAT works:
http://www.multilateration.com/surve...ateration.html