This week, Google told Business Insider that the microphone in its Nest Guard home security device was "never intended to be a secret."

The backlash had some people wondering: Do other Nest products have microphones they might not know about?

Google confirms with Business Insider that there's no microphone in any of its flagship Nest Learning Thermostat product line — but, as you may expect, there is one in all of its home security devices, including the Nest Cam camera and Nest Hello doorbell product lines.

Perhaps most surprising was that the current model of its smoke and carbon monoxide alarm — the Nest Protect — does contain a microphone for routine "sound checks," though this was also documented in spec sheets and support pages.

Last week, Google told Business Insider that the microphone in its Nest Guard security device was "never intended to be a secret," but had been erroneously omitted from the tech specs.

The revelation that the device unexpectedly had a microphone didn't sit well with plenty of consumers, and the backlash made its way to Capitol Hill. On Wednesday, California Senator Kamala Harris told Business Insider: "Americans shouldn't have to fear that the products in their home could be spying on them."

The incident left some people wondering: Do other Nest products have microphones they're not aware of?

A Google spokesperson confirmed with Business Insider this week that there is no microphone in the Nest Learning Thermostat, its flagship device. A teardown of the lower-cost Nest Thermostat E from 2017 further confirmed that there was no mic in that device.

Perhaps most surprising was that the second-generation model of the Nest Protect, its smoke and carbon monoxide alarm, does contain a microphone. Nest has made the microphone's existence clear in all of its marking materials and spec sheets.

On its support page, the company says that the microphone is there for routine alarm checks. Once a month, the device will automatically run a "sound check" and the microphone helps detect if its speaker and horn are working properly. Users can also run a manual "safety checkup" to test their Nest Protect, in which case the microphone is also enabled.

The Nest Learning Thermostat doesn't have a microphone, says Google. George Frey/Getty

In both scenarios, Google says the microphone is only on for a few seconds. and the audio data from those checks never leave a user's Nest Protect device, meaning it never goes to Google's servers.

Read more: Democratic presidential candidates are tearing into Google for the hidden Nest microphone, and calling for tech gadget 'ingredients' labels

Google also told us that all of its Nest camera products — Nest Cam IQ outdoor, Nest Cam IQ indoor, Nest Cam outdoor, Nest Cam indoor, and its smart doorbell, Nest Hello — have microphones. These were also clearly called out by the company from the beginning, it says.

With these confirmations from Google, it appears that no other Nest devices have unknown microphones, which may come as a relief to worried users.

The current-model Nest Protect smoke and carbon monoxide detector has a microphone, but only so it can automatically test the alarm, says Google. Nest

Still, the incident comes at a time when consumers are growing increasingly wary of major tech companies and their commitment to consumer privacy — mostly because of tech's history of repatedly failing to be upfront about privacy matters.

For Google, the revelation brings to mind previous privacy controversies, such as the 2010 incident in which the company acknowledged that its fleet of Street View cars collected personal data transmitted over consumers' unsecured WiFi networks, including emails, in what the search giant called an accident.

Here's a list of Nest products that contain a microphone:

Nest Guard Hub

Nest Protect (second-generation model)

Nest Cam IQ outdoor

Nest Cam IQ indoor

Nest Cam Outdoor

Nest Cam Indoor

Nest Hello

Got a tip? Contact this reporter via Signal at +1 (209) 730-3387, email at nbastone@businessinsider.com, or Twitter DM at @nickbastone.