"Every local police force could get a warrant to search your personal computer data without you ever knowing."
They can also get a warrant and come to your house and go through all of your stuff (including your personal computer) there. Of course you'd know, but not until it happened. There's no real "protection" from a legal search warrant.
The privacy implications and constitutional externalities are much larger (and easily abused) when it involves the interception of voice calls, emails, sms, locations, etc and now potentially all computer activity that happens in memory.
Wiretaps involve analyzing past data and actively monitoring new communications. Including every person you call or every website you visit. Police often have to delete 99%+ of intercepted data because it's irrelevant to the case.
That's different in many ways from a single physical search warrant on a house or computer.
And now they are becoming the go-to investigative tool for every criminal case...
I'd wager police also have to ignore 99%+ of the junk in your house when they execute a regular search warrant. They're going to look through your underwear drawer, but they're not actually going to confiscate all your underwear.
99% of the things sitting in any persons house at any moment is not as private as their ongoing phone calls, emails, websites they visit, etc. Nor does it simultaneously invade other peoples privacy in the process (any person they communicate with)... over a multi-month period.
Using your analogy, the 99% of things the police are supposed to ignore, such as their clothing drawers, does not carry equal weight in terms of privacy.
I'm not unique in having this position, lawyers/judges/courts view it as a much broader breach of privacy as well and they (often) require much stronger legal restrictions for the police than a standard search warrant.
Totally different level of scrutiny. Your home is your castle, and the police need to demonstrate cause to violate the sanctity of your home. The scope of warrants is usually limited as well. The police need to look for specific things. Also, unless the police demonstrate that you are associated with the crime, the police won't get a warrant to search your home because your brother committed a crime.
Third party requests for data are different, these often only require court orders or subpeonas, which don't receive nearly as much scrutiny. Your information may be accessed by an investigation relating to another person, for instance.
Your best privacy protection is to store stuff at home and access it remotely using an encrypted link, and to store your credential securely. (Think smartcard.)
That doesn't really scale does it. I imagine the tax man, however could set up some very nice cloud-based big data trawls for documents containing evidence of undeclared income.
They can also get a warrant and come to your house and go through all of your stuff (including your personal computer) there. Of course you'd know, but not until it happened. There's no real "protection" from a legal search warrant.