The Fourth Amendment guarantees freedom from "unreasonable" searches and seizures by government agents like police officers. That has generally meant that the police are required to obtain warrants before they arrest someone or search their property -- unless the police can point to a recognized exception to the warrant requirement. These exceptions include emergencies, situations where the person consents, and situations where evidence could quickly and easily be carried away or destroyed.
"When the government tracks the location of a cell phone," writes Chief Justice John Roberts, "it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone's user."
Colorado's express consent law provides that drivers, by virtue of driving on state roadways, have already consented to take a breath or blood test when an officer has probable cause to believe the person is impaired by alcohol or drugs. Refusal to take the test results in a revocation of the driver's license. Moreover, blood tests can be performed on people who are unconscious.
The international nongovernmental organization Human Rights Watch released a blockbuster report this week. It alleges that, in many cases federal law enforcement is tipping off state and local forces about information it may have learned by using constitutionally questionable practices. Such tips might not be admissible as evidence if brought before a court. Therefore, state and local police and prosecutors create false back stories for how they discovered the evidence.