Treat all downed power lines as hot.  Stay at least ten feet away from the lines.  If it is a transmission line from a tower, stay even farther away.

The neighborhood lines may be carrying anywhere from 220 volts, 60 Hz or higher and will develop a power field between the live downed line and the ground.  This field will have the highest voltage near the line as the inner most circle and have gradually reduced voltage circles out from the inner most circle.  If you place both your feet within one circle you are safe even though you are in the power field.  If you place separate feet into two different circles, the voltage will pass through you body and possibly injure or electrocute you.  To prevent this, place your feet as close together as possible and bunny hop out of the power field in a direct line so the possibility of your feet being in two different voltage circles is very small.  

Downed Power Lines on Vehicles

If there is no one in the vehicle, stay clear.

If someone is in the vehicle, they should be safe, unless it's a convertible, until the tires start burning.  Call 911 and inform them of the situation as soon after it occurs as possible so that the power company can come and turn off the power in that area.  If the tires start burning, the people should exit individually using the above bunny hop method, but this is a last resort.

Electrical Meters on the Outside of Houses

No one should attempt to remove such a device from the side of a building.  Power company personnel are only one equipped with the gloves and safety boots to prevent receiving a burn or worst during the process of removing the meter

Wireless Power Testers

Wireless tester are marketed at Lowe's and Home Depot for less than $20.00.  These are slightly larger than a pencil and emit a tone.  The one that uses the AA batteries last  somewhat longer than the one with the camera battery.  The power companies have not approved these for high voltage situations, but others have found them to be useful.