Source: Sierra Wireless.

This article was updated on March 16, 2016.

Internet of Things (IoT) darling Sierra Wireless (NASDAQ:SWIR) was on a tear in 2014. Its stock price shot up about 80%, making it one of the best-performing IoT stocks of 2014. But 2015 proved to be a very rough year for the company, with its stock price falling 67% for the full-year.

Sierra is a unique Internet of Things (IoT) pure play, but there are other tech companies that are making big bets on the IoT (while staying diversified in other businesses) and brining in much better gains. Let's take a quick look at four of them: 

Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL): Up 30% over the past 12 months
Alphabet's Google is clearly not an Internet of Things pure play, but it's still making very big strides in the space.

The company's self-driving cars are probably once of Google's most forward-facing IoT ambitions. Google is already a clear leader in the driverless space and has invested nearly $60 million in the technology already. 

Additionally, the company has also released its own open-source IoT platform, called Brillo. The system is similar to having Android on smartphones, except Brillo allows developers to add the software to IoT devices so that they easily communicate with one another. 

But Alphabet is also exploring even bigger IoT ideas like nanoparticles than can search out cancer in a person's blood stream. The company hopes to use the nanoparticles to report back to a wrist-worn device and send data about what they've found in a user's body. 

In its Q4 2015 earnings report, the company saw revenue increase 18% year-over-year, to $23.1 billion. (NASDAQ:AMZN): Up 52% over the past 12 months
Don't think Amazon is an IoT stock? Think again. Last year, the company showed off its Dash Replenishment Service (DSR) that allows device makers to load software into appliances so they can automatically order products from Amazon when needed. For example, some of Whirlpool's new washing machines can detect when they're out of detergent and will order more automatically. 

The company also made another stride into IoT late last year when it launched its Amazon Web Services (AWS) IoT platform. Lots of companies already rely on AWS for their websites, but the IoT portion will help companies store the data that small IoT devices send to the cloud to be analyzed. AWS IoT should make device-to-device communication easier through accessible and secure data, while giving device makers a reliable way to store IoT data.

But that's not all Amazon's doing. The company continues to make the smart home more of a priority. It's voice-activated Echo device launched last year, and has since expanded both its capabilities and the amount of devices that it can connect to. 

The company's Alexa virtual assistant can be used through the Echo to call an Uber vehicle, order pizza, check the weather, adjust your home's temperature and a host of other commands. With Echo, and the newly release Echo Dot and Echo Tap, Amazon is now the clear leader in the smart-home space.

Amazon's net sales increased by 22% in Q4 2015, to $35.7 billion. Of course, the company isn't earning most of its revenue from the IoT. But it's still making very bold moves into the space, and it appears to be paying off so far. 

NVIDIA (NASDAQ:NVDA): Up 40% over the past 12 months
NVIDA has moved quickly into the semi-autonomous and and autonomous car space over the past few years with great results. The company's Tegra K1 and new Tegra X1 helped power some of best autonomous car research, like the Audi A7 concept that drove itself from San Francisco to Las Vegas last year, as well as some of Google's autonomous cars.

NVIDIA also has its own autonomous driving platform, called Drive PX 2, which the company calls the "world's first in-car artificial intelligence supercomputer." Drive PX 2 can process 24 trillion deep learning operations every second, and helps self-driving cars have their own situational awareness. Already more than 50 carmakers are using NVIDIA's autonomous driving platform. 

But the company isn't just looking to autonomous cars to drive its IoT growth. NVIDIA CEO Jen-Hsun Huang said last year that, "We see a future of autonomous cars, robots, and drones that see and learn, with seeming intelligence that is hard to imagine." In its fiscal Q4 2016, NVIDIA posted record revenue of $1.4 billion, up 12% year-over-year. And the company reported full-year revenue of $5 billion, an increased of 7% year-over-year. While the company certainly has its hands in more than just the Internet of Things, its IoT ambitions will help drive further growth.

Apple (NASDAQ:AAPL): Down 18% over the past 12 months
Sure, Apple's stock is down right now, but it doesn't come anywhere near Sierra's 60% fall over the past 12 months

Despite Apple's fall, the company's recent dominance in the wearable tech space has pushed the company firmly into the Internet of Things space. Apple took the No. 2 spot for overall wearable tech shipments in 2015, just nine months after it debuted its Apple Watch. 

In the smartwatch market, which is a subset of the IoT, Apple took two-thirds of all the smartwatch sales in 2015 -- and it's expected to keep more than half of smartwatch market share until about 2019. While consumers may still be a bit skeptical about smartwatches, it's clear Apple's already making its mark in the space and will likely continue its dominance for the foreseeable future. 

In Q1 2016, Apple reported revenue of $75.9 billion. While Apple is just getting started in IoT, the company's resources and current dominance in the smartwatch space have solidified its leadership position in the Internet of Things.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.