Corporate insiders sell their own companies' stock for a number of reasons.

They might need the cash for a big personal purchase such as a new house or yacht, or they might need it to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price.

Other times they sell because they think their stock is overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share.

But insiders usually buy their own shares for one reason: They think the stock is a bargain and has tremendous upside.

The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

Stocks with notable insider activity is something that I tweet about on a regular basis. These are also the exact type of stocks that I love to trade and alert in real time.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks.

Akamai Technologies

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One technology stock that insiders are jumping into here is Akamai Technologies (AKAM) - Get Report , which provides cloud services for delivering, optimizing and securing content and business applications over the Internet in the U.S. and internationally. Insiders are buying this stock into modest weakness, since shares have dropped by 7.2% over the last six months.

Akamai Technologies has a market cap of $9.3 billion and an enterprise value of $8.7 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 30 and a forward price-to-earnings of 17.2. Its estimated growth rate for this year is 6.7%, and for next year it's pegged at 13.4%. This is a cash-rich company, since the total cash position on its balance sheet is $837.87 million and its total debt is $623.48 million.

The CEO just bought 19,497 shares, or about $999,000 worth of stock at $51.28 per share. From a technical perspective, Akamai Technologies is currently trending above its 50-day moving average and below its 200-day moving average, which is neutral trendwise. This stock has been uptrending over the last few weeks, with shares moving higher off its low of $48.88 a share to its intraday high on Wednesday of $53.81 a share. During that uptrend, this stock has been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of Akamai Technologies within range of triggering a big breakout trade.

If you're bullish on Akamai Technologies, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $51.04 a share and then once it breaks out above some near-term overhead resistance levels at $54 to $55 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average volume of 2.04 million shares. If that breakout triggers soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $57.50 to its 200-day moving average of $58.14, or even $60 a share.

General Electric

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Another industrial goods player that insiders are active in here is General Electric (GE) - Get Report , which operates as an infrastructure and financial services company worldwide. Insiders are buying this stock into modest strength, since shares have risen by 3.5% over the last three months.

General Electric has a market cap of $278 billion and an enterprise value of $447 billion. This stock trades at a reasonable valuation, with trailing price-to-earnings of 40.9 and a forward price-to-earnings of 17.2. Its estimated growth rate for this year is 15.3%, and for next year it's pegged at 15.9%. This is not a cash-rich company, since the total cash position on its balance sheet is $9.30 billion and its total debt is $186.05 billion. This stock currently sports a dividend yield of 3.1%.

The CEO just bought 67,600 shares, or about $2 million worth of stock, at $29.59 per share.

From a technical perspective, General Electric is currently trending above its 200-day moving average and just below its 50-day moving average, which is neutral trendwise. This stock has just started to trend back above its 20-day moving average of $30.08 a share. This spike to the upside is now quickly pushing shares of General Electric within range of triggering a big breakout trade above some key near-term overhead resistance levels.

If you're bullish on General Electric then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $30.08 a share or above some more key near-term support at $29.25 a share and then once it breaks out above some near-term overhead resistance levels at its 50-day moving average of $30.66 to $30.75 a share and then above $31.25 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average action of 31.76 million shares. If that breakout hits soon, then this stock will set up to re-test or possibly take out its next major overhead resistance level at its 52-week high of $32.05 a share. Any high-volume move above $32.05 will then give this stock a chance to tag $35 to $40 a share.

From a fundamental perspective, GE is a holding in Jim Cramer's Action Alerts PLUS charitable portfolio. He and Research Director Jack Mohr wrote recently: 

We believe the company has made strong progress on its key transformation initiatives including the sale of its capital assets (which is 80% complete), integration of Alstom (the global juggernaut in renewable energy that should lift earnings by 10% over the next two years) and GE Digital (which has grown from zero to $5 billion in five years and is expected to continue growing at a 30% annualized clip). These catalysts, paired with a juicy dividend yield (now 3.2%) and buyback program, support our bullish long-term view.

Baxter International

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One healthcare player that insiders are jumping into here is Baxter International (BAX) - Get Report , which provides a portfolio of renal and hospital products. Insiders are buying this stock into notable strength, since shares have spiked by 14.8% over the last six months.

Baxter International has a market cap of $24 billion and an enterprise value of $23.5 billion. This stock trades at a fair valuation, with a trailing price-to-earnings of 6.1 and a forward price-to-earnings of 22.7. Its estimated growth rate for this year 18.8%, and for next year it's pegged at 15.9%. This is barely a cash-rich company, since the total cash position on its balance sheet is $3.44 billion and its total debt is $3.36 billion. This stock currently sports a dividend yield of 1.2%.

The CEO just bought 11,691 shares, or about $499,000 worth of stock, at $42.75 per share.

From a technical perspective, Baxter International is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been downtrending a bit over the last few weeks, with shares falling sharply off its high of $46.95 a share to its recent low of $42.57 a share. During that downtrend, this stock has been making mostly lower highs and lower lows, which is bearish technical price action. That said, this stock is still inside of an overall monster uptrend that dates back to the start of the year.

If you're in the bull camp on Baxter International, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $42.96 a share or above more near-term support at $42.57 a share and then once it breaks out above some near-term overhead resistance levels at $44 to its 20-day moving average of $44.61 a share with volume that hits near or above its three-month average action of 9.73 million shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance level at its 52-week high of $46.95 a share.

Seritage Growth Properties

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Another stock that insiders are loading up on here is Seritage Growth Properties (SRG) - Get Report , which is a publicly owned real estate investment trust. Insiders are buying this stock into notable strength, since shares have trended higher by 22.8% over the last six months.

Seritage Growth Properties has a market cap of $1.4 billion and an enterprise value of $2.4 billion. This stock trades at a premium valuation, with a forward price-to-earnings of 24.2. Its estimated growth rate for next year is -17%. This is not a cash-rich company, since the total cash position on its balance sheet is $62.12 million and its total debt is $1.14 billion. This stock currently sports a dividend yield of 2.2%.

A beneficial owner just bought 37,700 shares, or about $1.65 million worth of stock, at $43 per share.

From a technical perspective, Seritage Growth Properties is currently trending above its 200-day moving average and below its 50-day moving average, which is neutral trendwise. This stock has been downtrending over the last two months, with shares falling sharply off its high of $57.31 a share to its recent low of $42.47 a share. During that downtrend, shares of Seritage Growth Properties have been making mostly lower highs and lower lows, which is bearish technical price action.

If you're bullish in Seritage Growth Properties, then I would look for long-biased trades as long as this stock is trending above some near-term support levels at $42.47 a share or above its 200-day moving average of $41.95 a share and then once it breaks out above some near-term overhead resistance levels at $44.69 to around $46 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 312,803 shares. If that breakout fires off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at its 20-day moving average of $49.05 to its 50-day moving average of $50.35 a share.

First Data

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My final stock with some large insider buying is technology player First Data (FDC) - Get Report , which provides electronic commerce solutions for merchants, financial institutions and card issuers worldwide. Insiders are buying this stock into notable weakness, since shares have dropped by 24.6% over the last six months.

First Data has a market cap of $11.30 billion and an enterprise value of $29.9 billion. This stock trades at a cheap valuation, with a forward price-to-earnings of 8.15. Its estimated growth rate for this year is 87.1%, and for next year it's pegged at 16%. This is not a cash-rich company, since the total cash position on its balance sheet is $311 million and its total debt is $19.46 billion.

A director just bought 100,000 shares, or about $1.06 million worth of stock, at $10.59 to $10.63 per share.

From a technical perspective, First Data is currently trending above both its 50-day and 20-day moving averages, which is bullish. This stock recently formed a double bottom chart pattern, after shares found some buying interest at $10.36 to $10.44 a share. Following that potential bottom, this stock has now started to spike higher back above both its 20-day moving average of $11.25 a share and its 50-day moving average of $12.08 a share with strong upside volume flows. That spike is now quickly pushing shares of First Data within range of triggering a big breakout trade.

If you're bullish on First Data, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $11.25 a share or above those recent double bottom support levels and then once it breaks out above some near-term overhead resistance levels at $13 to $13.50 a share and then above more key resistance at $14 to $14.75 a share with volume that hits near or above its three-month average action of 4.57 million shares. If that breakout materializes soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $17 to $17.45 a share, or even its 52-week high of $17.99 a share.

Disclosure: This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.