Sense Labs Inc., a Cambridge startup developing an Internet-connected home electricity monitor, has added robotic vacuum maker iRobot as an investor, raising another $1 million to help expand manufacturing and sales.

The new cash adds modestly to the roughly $14 million investment round the startup closed last fall, led by investors from the electric-utility and oil industries. Sense has now raised a total of $20 million.

The company’s device, which sells for $299, attaches to a home’s main electric panel to analyze the electricity consumption patterns of appliances, lights, and household gadgets. Sense started selling the product online last year.

The company is also beginning to connect its gadget with other with other Internet-enabled “smart home” devices, such as remote-controlled lights and software-enabled appliances, a growing consumer category.

Get Talking Points in your inbox:
An afternoon recap of the day’s most important business news, delivered weekdays.

Sense’s focus on blending complex hardware and software in a consumer-friendly device made iRobot a good match for it, said Sense chief executive Mike Phillips.

“It’s a really hard technology underneath. It’s a consumer-facing bit of hardware. And it’s a new product category. All three of those things are hard — hard to the nth degree,” Phillips said. “iRobot’s a good example of that, too. They did the same thing.”

Sense has about 25 employees, and recently added new leaders for its sales and manufacturing operations, Phillips said.

The Sense device measures a home’s electric pulses about 1 million times per second, and sends the data over a wireless Internet connection to the company’s software, which helps decode the electric-use “fingerprint” of each device.

A heating element, for example, has a fairly constant pattern of electricity use compared with a refrigerator motor, which draws a distinctive spike of electricity when it first starts spinning.

Sense’s software can help homeowners compare the energy-use patterns in their home by deducing how long the TV has been on each week, or noticing when the lights in the garage were left on. The company believes its device will become even more desirable when it can connect with other smart-home products.

“There are very few opportunities in the home that actually have true platform-like potential,” said Hanns Anders, an investment manager for iRobot Ventures. “It has the potential to both inform and feed off a lot of other products, including robotics.”

Sense is taking a first step toward that capability by integrating its device with IFTTT, an Internet service that lets people create their own simple connections between devices. For instance, a user might be able to use IFTTT to instruct Sense to send someone a text message when a load of laundry is done.

Widespread device integrations will likely depend on appliance and software manufacturers settling on common technical standards that allow devices to more easily talk to each other, Phillips said. But the company can still work with individual gadgets and manufacturers, he said.

Curt Woodward can be reached at [email protected]. Follow him on Twitter @curtwoodward.