The records, from more than 125 police agencies in 33 states, reveal:

• About one in four law-enforcement agencies have used a tactic known as a “tower dump,” which gives police data about the identity, activity and location of any phone that connects to the targeted cellphone towers over a set span of time, usually an hour or two. A typical dump covers multiple towers, and wireless providers, and can net information from thousands of phones.

• At least 25 police departments own a Stingray, a suitcase-size device that costs as much as $400,000 and acts as a fake cell tower. The system, typically installed in a vehicle so it can be moved into any neighborhood, tricks all nearby phones into connecting to it and feeding data to police. In some states, the devices are available to any local police department via state surveillance units. The federal government funds most of the purchases, via anti-terror grants.