Connected devices and the Internet of Things are all the rage these days. Companies of all types are pumping out new products and technologies at breakneck speed in hopes of cashing in on this fast-growing market. By 2019, the Internet of Things, or IoT, market will more than double the size of the smartphone, PC, tablet, connected car, and wearable markets combined, according to Business Insider. So how can investors grab a piece of the action? Below, Fool contributors explain why Google (NASDAQ:GOOG), General Electric (NYSE:GE), and Intel (NASDAQ:INTC) are three of the best stocks to invest in the Internet of Things.

Tim Brugger: Leading the way in the explosion of the Internet of Things, according to industry pundits, will be the advent of the "smart home." Already, consumers can control some basic household functions via connected devices, including remotely operating lights and monitoring security devices, but that's just the tip of what will become a giant iceberg. And Google is positioning itself as the smart-home IoT provider to beat.

Google made a $3.2 billion splash when it acquired smart home device manufacturer Nest earlier this year. Nest is a leading provider of thermostats that "learn" based on user behavior, as well as high-end smoke and CO2 detectors, which are both areas expected to lead the way in smart-home growth over the next five years. Smart homes will make up over a quarter of IoT revenue by 2019, according to a recent report, climbing to an estimated $490 billion in annual sales. And Nest is just one of several arrows in Google's IoT quiver.

In June, Google -- via Nest -- bought cloud-based smart security camera maker Dropcam, and followed that up with last month's deal for Revolv. Revolv, in particular, separates Google from the smart-home masses by addressing one of the budding industry's biggest challenges: a way for multiple smart devices within a home to "talk" to each other. Smart homes will lead the way in IoT adoption over the next several years, and Google is positioned to dominate. IoT in general, and smart homes in particular, will soon light a fire under Google's languishing stock price.

Anders Bylund: When looking for great investments in The Next Big Thing (tm), century-old companies with an industrial past rarely come to mind. But when thinking about the Internet of Things megatrend, it would be crazy to ignore good old General Electric. The GE you see today is a far cry from the heavy-industry giant your grandfather grew up with.

Yes, GE has a tight focus on industrial operations, with a long-term goal to reap 75% of its earnings from this sector. Today, only 60% of GE's earnings arrive from its industrial side, with the remainder piped in via banking division GE Capital. But heavy machinery has changed over the last 100 years. General Electric makes a selling point out of the sensor-packed nature of its industrial designs. Whether you're buying airplane engines, giant gas turbines, or fully functional railroad locomotives, GE's models are likely to collect more data about every operational detail than the competition does.

Analyzing these huge data flows can unlock hidden patterns and support actionable business decisions. GE's airplane parts deliver so much granular data that a deep analysis can shave maintenance cycles off from some carrier routes while suggesting cost-saving adjustments to planes on more stressful itineraries. These adjustments make for better operation, lower overall maintenance costs, and a more attractive outcome for the airline -- which means more orders from plane builders.

Source: GE.

This data collection is powered by thousands of sensors tied together by wireless networks. It's how GE is turning the Internet of Things into a real business advantage. The company has started a software division to support these hardware bits, and even coined its own term for this particular niche. The Internet of Things -- sorry, I mean the Industrial Internet -- will help General Electric stay relevant in the new era of modern industry. And it still looks like a great investment for the very long term.

Tamara Walsh: Intel might have been late to the mobile revolution, but it won't miss out on the more recent connected devices phenomenon that is the Internet of Things. The chipmaker is deploying products and technologies that help connect items like wearable devices and vehicles to the Internet in a fast and seamless way. The IoT universe can be broken into four distinct categories: things (that are connected to the Internet), gateways, network and cloud, and services.

From tiny wireless modems to data center management, Intel is uniquely positioned to dominate this burgeoning market. For example, the tech giant has designed special processors and chipsets intended to power wearables and other Internet of Things devices. Intel could also capitalize on this market through back-end tech such as its Intel Edison mini technology-based computer, which features built-in wireless that is housed in an SD card form factor. Moreover, the power and relatively small size of these chips and processors should help position Intel as a leader in the IoT space.

Protecting important data will be a key focus as more devices are connected to the IoT. With innovative solutions already in the works, Intel could take the lead in this area as well. Thanks to Intel's purchase of McAfee in 2011, the company already offers a broad range of security products designed with the IoT market in mind. Some of these include McAfee Endpoint Encryption and McAfee Embedded Control, which can be deployed on connected devices, gateways, and network and cloud infrastructure.

Ultimately, this multichannel approach proves Intel has what it takes to become a key player in the Internet of Things space.