Advances in technology have given police agencies expanded surveillance capabilities. But used in secret or indiscriminately, technology presents major threats to privacy and civil rights and can erode public trust in law enforcement.

New and more invasive technologies, such as mass cellphone tracking, are being put into service by police agencies with little or no public discussion. That’s unfortunate. Communities should be able to debate and decide how much privacy, if any, they are willing to give up in pursuit of public safety.

The American Civil Liberties Union pf California has produced a guide for communities on how to evaluate surveillance proposals and how to put in place security and civil liberties safeguards before these new tools are used. The ACLU’s approach to vetting new technologies is so pragmatic that cities, counties and law enforcement agencies would be foolish not to embrace it.

For example, the guide urges communities and police departments to figure out what problem the surveillance is intended to address and whether that technology is really the best tool for the job. There may be a temptation to roll out the latest whiz-bang gadget, especially when it’s paid for with federal grants, without considering the practical value and implementation costs, or developing protocols to measure results or get feedback.

To ensure a proper review for every new technology, cities and counties in California should require that law enforcement agencies within their jurisdiction have a formal surveillance technology review and use process. That policy should spell out how communities will be consulted on new programs; establish rules for who can use the data that are collected and why; and guard against abuse or security breaches of personal information.

These new technologies could result in safer, more secure communities — if managed correctly. But “trust us” is not enough.