It's tough to be a device maker. Consumer preferences can be fickle, and cheaper competition is an ever-present threat. Selling a steady slew of gadgets can be fantastically profitable but it can also be downright brutal.

Hewlett-Packard (NYSE:HPQ), Samsung (NASDAQOTH:SSNLF), and Fitbit (NYSE:FIT) are three of the most interesting stocks in the space. It's not clear that they're fantastic investments, but all three are worthy of being watched.

Image: Hewlett-Packard

Hewlett-Packard is about to create a pure-play device company
There's much more to Hewlett-Packard than just PCs. The tech giant is involved in numerous industries, including servers, software, cloud computing and enterprise services. This wide-ranging involvement, however, may be holding the company back. In an effort to sharpen its focus, Hewlett-Packard will cleave itself in two later this year, forming two separate public companies in the process.

Hewlett-Packard Enterprise will contain Hewlett-Packard's software and service business segments. HP will be made up of its PC and printer businesses. That makes it an intriguing stock to anyone interested in devices. With Dell now a privately held company, the only other public PC companies left trade on foreign exchanges -- as the second-largest PC vendor, HP will become the best way to gain exposure to Windows PCs.

Unfortunately for HP, the market for traditional PCs appears to be in inexorable decline. According to IDC, PC shipments dropped 6.7% on an annual basis in the first quarter. That was better than expected, but it still stands in sharp contrast to smartphones, which continue to experience growth. IDC expects smartphone shipments to increase 11.3% in 2015.

Nevertheless, HP could be a great investment if shares are cheap enough. Currently, Hewlett-Packard trades with a below-market multiple of around 12.50. Hewlett-Packard Enterprise will likely get a higher multiple, as its business segments seem to hold greater, long-term promise. If HP gets a single-digit multiple, it could reward shareholders even if its business is in decline.

Going into the split, investors interested in firms that make devices should keep a close eye on Hewlett-Packard.

Samsung has suffered from increasing competition
Samsung remains the world's largest smartphone vendor, but its business appears to be in a precarious position. Just two years ago Samsung was riding high, earning billions from sales of its flagship Galaxy smartphones.

But the market has changed -- competition has intensified, and Samsung, while still profitable, has seen its sales and its earnings plunge. Last quarter, Samsung's total earnings fell 39%, while earnings from its mobile division in particular fell 57%. In Asia, Samsung is facing the threat of competitors releasing a slew of ever-better, low-cost devices. And around the globe, Apple appears to be taking share at the high end.

Still, Samsung is interesting for one reason: It's absurdly cheap, to the point where it could be dramatically undervalued. At current levels, the stock trades with a trailing price-to-earnings ratio of just 9, and about one-third of its market cap is in cash. Samsung's problems appear challenging, but if it can turn its business around, shares could bounce back.

Fitbit is profitable, but its moat is highly suspect
Fitbit's fitness trackers are in demand. The company, which entered the public markets earlier this month, has seen rapid growth and has sold 21 million fitness trackers to date. IDC believes the overall market will continue to grow, jumping to 114 million devices shipped by 2018. Last year, Fitbit generated more than $745 million in revenue, up from $76.4 million in 2012. It brought in $131.8 million in net income, up from a loss of $51.6 million in 2013.

But the problem for Fitbit is competition, and its reliance on a single product. Admittedly, Fitbit sells several different models, but they're all fundamentally the same -- tracking the user's activity level and sleep. Smartwatches, including the Apple Watch, already offer similar features, and they should continue to improve over time. At the same time, Fitbit faces a lot of competition at the low-end -- Xiaomi's Mi Band, for example, retails for just $20. Fitbit has brand recognition, and arguably the best products in its class, but it doesn't have much of an ecosystem to keep its customers loyal.

Due to this conflict -- promising growth, but a competitive advantage that's questionable at best -- Fitbit may not be an overwhelmingly promising investment, but its a device maker worth watching.