A helicopter hovering or circling overhead is one of the most-asked "what is that?" questions — and usually has an ordinary answer. Many helicopters broadcast ADS-B just like aeroplanes, so AeroScope can often tell you what it is and what it’s doing. Here’s how, and the honest exceptions.
Circling a wide area, often at night, supporting an incident on the ground. Some forces limit what they broadcast.
Orbiting a traffic incident, event or breaking story to get a stable camera shot.
Transiting fast and low, or landing at a scene or hospital. Time-critical, so direct routing.
Transit or training. Flagged from ICAO hex and callsign — see military over my house.
Slow, methodical grid or line-following for power lines, pipelines, mapping or aerial photography.
Point-to-point transport or sightseeing, often broadcasting full identity.