Apple has yet to confirm the hidden hardware but according to "people familiar with the situation", the California-based tech giant has "internally discussed" using the sensor to trigger specific actions when your home gets too hot or too cold.
There's talk of the HomePod Mini switching on your heating when it gets chilly, or triggering a fan when your room gets stuffy. The sensor is currently dormant but could – in theory – be activated through a software upgrade, providing new smart home functionality.
Apple has form when it comes to secret features. It slipped a Bluetooth chip into its 2008 iPod Touch – but waited until 2009 to confirm the secret and enable Bluetooth connectivity.
- Save big with this week's best HomePod and HomePod mini deals
The HomePod mini launched last November and is one of the best-sounding smart speakers we've heard at this price. It already offers a clever home intercom system, but it seems Apple could be planning to ramp up its smart home appeal in an effort to go toe to toe with Amazon and Google.
According to some experts, Apple lacks a "unifying strategy" around smart home tech. While there are plenty of third-party lightbulbs, thermostats, locks and plugs that work with the company's smart home system, Apple HomeKit, Apple does not currently make its own smart home hardware beyond the HomePod Mini and the Apple TV streaming box (soon to be replaced by the new Apple TV).
The company was tipped to hold an event on Tuesday 23rd March to unveil its latest AirPods 3, iPad and AirTags but that now seems unlikely. Last week Apple analyst Ming Chi-Kuo said the AirPods 3 were delayed until Autumn, while a new report by Bloomberg points to a new iPad in April.
Read our in-depth review of the Apple HomePod Mini
Check out this week's best iPhone deals and cheapest prices
Discover the best wireless speakers for all budgets