Criminal defendants have caught on. Recently, a suspect in a Manhattan felony, speaking on a recorded jailhouse call, noted that “Apple and Google came out with these softwares” that the police cannot easily unlock.

Apple, Google and other proponents of full-disk encryption have offered several rationales for this new encryption technology. They have portrayed the new policy as a response to the concerns raised by Edward J. Snowden about data collection by the National Security Agency. They say full-disk encryption makes devices generally more secure from cybercrime. And they assert that, if the companies had master encryption keys, then repressive governments could exploit the keys.

These reasons should not be accepted at face value. The new Apple encryption would not have prevented the N.S.A.’s mass collection of phone-call data or the interception of telecommunications, as revealed by Mr. Snowden. There is no evidence that it would address institutional data breaches or the use of malware. And we are not talking about violating civil liberties — we are talking about the ability to unlock phones pursuant to lawful, transparent judicial orders.

In the United States, Britain, France, Spain and other democratic societies, the legal system gives local law enforcement agencies access to places where criminals hide evidence, including their homes, car trunks, storage facilities, computers and digital networks.

Carved into the bedrock of each of these laws is a balance between the privacy rights of individuals and the public safety rights of their communities. For our investigators to conduct searches in any of our jurisdictions, a local judge or commissioner must decide whether good cause exists. None of our agencies engage in bulk data collection or other secretive practices. We engage in targeted requests for information, authorized after an impartial, judicial determination of good cause, in which both proportionality and necessity are tested.

It is this workable balance that proscribes the operations of local law enforcement in our cities, and guides our residents in developing their expectations of privacy. But in the absence of laws that keep pace with technology, we have enabled two Silicon Valley technology companies to upset that balance fundamentally.

The Evanston case is just one example. In France, smartphone data was vital to the swift investigation of the Charlie Hebdo terrorist attacks in January, and the deadly attack on a gas facility at Saint-Quentin-Fallavier, near Lyon, in June. And on a daily basis, our agencies rely on evidence lawfully retrieved from smartphones to fight sex crimes, child abuse, cybercrime, robberies or homicides.