DELAFIELD, Wis. (Stockpickr) -- 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 the cash 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.

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.

Alere

One health care player that insiders are active in here is Alere (ALR) , which provides point-of-care diagnostics and services for infectious disease, cardiometabolic disease, and toxicology in the U.S. and internationally. Insiders are buying this stock into strength, since shares have ripped higher by 23.7% over the last six months.

Alere has a market cap of $4.5 billion and an enterprise value of $7.5 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 28.2 and a forward price-to-earnings of 18.6. Its estimated growth rate for this year is 25%, and for next year it's pegged at 27.4%. This is not a cash-rich company, since the total cash position on its balance sheet is $465.05 million and its total debt is $3.60 billion.

The CFO just bought 20,000 shares, or about $986,000 worth of stock, at $49.33 per share.

From a technical perspective, Alere is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending a bit over the last month, with shares moving higher from its low of $48.08 to its recent high of $53.48 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 Alere within range of triggering a big breakout trade above some key near-term overhead resistance levels.

If you're bullish on Alere, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $50.89 a share and then once it breaks out above some near-term overhead resistance levels at $53.48 to its 52-week high of $54.58 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 546,667 shares.

If that breakout hits soon, then this stock will set up to enter new 52-week-high territory, which is bullish technical price action. Some possible upside targets off that breakout are $60 to $65 a share.

Twitter

A social media player that insiders are jumping into here is Twitter(TWTR) - Get Report, which operates as a global platform for public self-expression and conversation in real time. Insiders are buying this stock into large weakness, since shares have dropped by 37.6% over the last six months.

Twitter has a market cap of $19.7 billion and an enterprise value of $17.7 billion. This stock trades at a reasonable valuation, with a forward price-to-earnings of 46.28. Its estimated growth rate for this year is 142.9%, and for next year it's pegged at 88.2%. This is a cash-rich company, since the total cash position on its balance sheet is $3.56 billion and its total debt is $1.60 billion.

The CEO just bought 31,627 shares, or about $875,000 worth of stock, at $27.67 per share.

From a technical perspective, Twitter is currently trending well below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending badly over the last four months and change, with shares falling from its high of $53.49 to its recent low of $26.87 a share. During that downtrend, shares of Twitter have been making mostly lower highs and lower lows, which is bearish technical price action. That said, this stock has recently started to rebound off that $26.87 low and it's now moving within range of triggering a near-term breakout trade.

If you're in the bull camp on Twitter, then I would look for long-biased trades as long as this stock is trending above some near-term support levels at $28 or above its recent low of $26.87 a share and then once it breaks out above some near-term overhead resistance at $30 a share with volume that hits near or above its three-month average action of 21.73 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 levels at its 20-day moving average of $32.67 to its 50-day moving average of $34.41 a share.

Virtu Financial

One financial player that insiders are loading up on here is Virtu Financial(VIRT) - Get Report, which provides market making and liquidity services to the financial markets worldwide. Insiders are buying this stock into modest weakness, since shares have dropped by 7.2% over the last three months.

Virtu Financial has a market cap of $2.9 billion and an enterprise value of $785 million. This stock trades at a fair valuation, with a trailing price-to-earnings of 39 and a forward price-to-earnings of 14.7. Its estimated growth rate for next year is pegged at 10.1%. This is a cash-rich company, since the total cash position on its balance sheet is $2.88 billion and its total debt is $1.37 billion.

The chairman of the board just bought 200,000 shares, or about $4.13 million worth of stock, at $20.66 per share.

From a technical perspective, Virtu Financial is currently trending below both its 50-day and 20-day moving averages, which is bearish. This stock has been downtrending over the last two months, with shares moving lower from its high of $24.77 to its recent low of $20.13 a share. During that downtrend, this stock has been making mostly lower highs and lower lows, which is bearish technical price action. That said, shares of Virtu Financial have now started to rebound off its recent low of $20.13 and it's beginning to move within range of triggering a near-term breakout trade.

If you're bullish on Virtu Financial, then I would look for long-biased trades as long as this stock is trending above its recent low of $20.13 a share and then once it breaks out above some near-term overhead resistance at $21.61 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average volume of 431,702 shares. If that breakout gets started 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 $22.91 to its 50-day moving average of $23.23 a share.

Comstock Resources

One energy player that insiders are snapping up a decent amount of stock in here is Comstock Resources(CRK) - Get Report, which acquires, develops, explores, and produces oil and natural gas properties in the U.S. Insiders are buying this stock into massive weakness, since shares have plunged by 64% over the last six months.

Comstock Resources has a market cap of $92.1 million and an enterprise value of $1.3 billion. This stock trades at a reasonable valuation, with a price-to-sales of 0.19 and a price-to-book of 0.11. Its estimated growth for the next quarter is -510.5%, and for next year it's pegged at 4.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $130.21 million and its total debt is $1.38 billion.

A beneficial owner just bought 1,255,895 shares, or about $1.59 million worth of stock, at $1.10 to $1.25 per share.

From a technical perspective, Comstock Resources is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending over the last few weeks, with shares moving higher from its low of 99 cents per share to its intraday high on Tuesday of $2.13 a share. During that uptrend, shares of Comstock Resources have been consistently making higher lows and higher highs, which is bullish technical price action. This uptrend has now pushed this stock within range of triggering a near-term breakout trade above some key overhead resistance levels.

If you're bullish on Comstock Resources, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $1.60 a share and then once it breaks out above some near-term overhead resistance levels at $2.30 to its 50-day moving average of $2.57 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 2.33 million shares. If that breakout begins soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $3.30 to $4 a share.

Pinnacle Foods

One final stock with some decent insider buying is Pinnacle Foods (PF) , which manufactures, markets, and distributes branded convenience food products in North America. Insiders are buying this stock into large strength, since shares have jumped higher by 27.8% over the last six months.

Pinnacle Foods has a market cap of $5.3 billion and an enterprise value of $7.5 billion. This stock trades at a fair valuation, with a trailing price-to-earnings of 21.5 and a forward price-to-earnings of 22.2. Its estimated growth for this year is 9.8%, and for next year it's pegged at 8.4%. This is not a cash-rich company, since the total cash position on its balance sheet is $53.36 million and its total debt is $2.30 billion. This stock currently sports a dividend yield of 2.1%.

A director just bought 20,000 shares, or about $909,000 worth of stock, at $45.48 per share. From a technical perspective, Pinnacle Foods is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending strong over the last six months, with shares moving higher from its low of $35.16 to its recent high of $48.13 a share. During that uptrend, this stock has been making mostly higher lows and higher highs, which is bullish technical price action.

If you're bullish on Pinnacle Foods, then I would look for long-biased trades as long as this stock is trending above some key near-term support levels at $44.73 to $44.22 a share and then once it breaks out above some near-term overhead resistance levels at $46.14 to $46.88 a share and then above its all-time high of $48.13 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 volume of 1.13 million shares.

If that breakout materializes soon, then this stock will set up to enter new all-time-high territory, which is bullish technical price action. Some possible upside targets off that breakout are $55 to $60 a share.

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