As Amazon.com Inc. and Google work to place their smart speakers at the center of the internet-connected home, both technology giants are expanding the amount of data they gather about customers who use their voice software to control other gadgets.

For several years, Amazon and Google have collected data every time someone used a smart speaker to turn on a light or lock a door. Now they're asking smart-home gadget makers such as Logitech and Hunter Fan Co. to send a continuous stream of information.

In other words, after you connect a light fixture to Alexa, Amazon wants to know every time the light is turned on or off, regardless of whether you asked Alexa to toggle the switch. Televisions must report the channel they're set to. Smart locks must keep the company apprised whether or not the front door bolt is engaged.

This information may seem mundane compared with smartphone geolocation software that follows you around or the trove of personal data Facebook Inc. vacuums up based on your activity. But even gadgets as simple as light bulbs could enable tech companies to fill in blanks about their customers and use the data for marketing purposes.