Nest thermostats will warn of possible problems with your AC or furnace

They can detect patterns that hint at breakdowns.

You might not have to wait until your home is frigid to find out that there's a problem with your furnace. Google has started testing a Nest thermostat feature that sends email alerts when the device detects unusual patterns in your HVAC system. If it's taking an oddly long time to warm up your house, you might get a notice well before there's a full-fledged breakdown.

People in a handful of cities (Atlanta, Boston, Denver, Las Vegas and San Diego) will also get help contacting professionals through Handy, so you might not have trouble booking a service appointment.

HVAC warnings aren't completely new. Users have received alerts for more immediate problems. However, Google is now focusing on symptoms that may take a long time for humans to spot. In a sense, it's offering a peek at a future where your smart home does more to anticipate problems and help fix them before it's too late.