Can you triangulate a cell phone without making a call?

Every cell tower knows where it is. Your phone is always sending "ping" signals back and forth to the towers around it, so they can negotiate over which tower gives the best signal. That's how the system knows to hand your call off from one tower to the next if you're driving down the highway (for example). The cell system knows which tower your cell phone is talking to (otherwise it couldn't send you calls). So the system knows you are within range of that cell tower's location. Depending on the specific tower, that range could be from a fraction of a mile up to a few miles. The tower can also measure how long it takes to get a response from your phone, and use that to estimate how far away you are. That puts you on the edge of a circle that distance from the tower. Usually your phone can be heard by multiple cell towers. If two can hear you, then you're on the edge of each of 2 circles, and two circles can only meet at 2 points, so you must be at one of those 2 points. If a third tower can hear you, its circle can only meet the others at one point, so there you are. Emergency services (like 911) can get this information from the cell towers. The information exists whenever your phone is on and in range of a tower, whether you're making a call or not. The information is not meant to be publicly accessible.