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.

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.

aTyr Pharma

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One stock with some decent insider buying is biotherapeutics player aTyr Pharma (LIFE) - Get Report , which engages in the discovery and clinical development of Physiocrine-based therapeutics for patients suffering from severe and rare diseases. Insiders are buying this stock into massive weakness, since shares have plunged by 65% over the last six months.

aTyr Pharma has a market cap of $92.3 million and an enterprise value of -$11.3 million. This stock trades at a fair valuation, with a price-to-book of 0.71. Its estimated growth rate for this year is 2.6%, and for next year it's pegged at -11.5%. This is a cash-rich company, since the total cash position on its balance sheet is $108.80 million and its total debt is $5.95 million.

A director just bought 85,000 shares, or about $273,000 worth of stock at $3.22 per share. That same director also just bought 32,659 shares, or about $116,000 worth of stock at $3.45 per share.

From a technical perspective, aTyr Pharma is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending strong over the last few trading sessions, with shares moving higher off its new 52-week low of $3.03 a share to its intraday high on Wednesday of $4.02 a share. During that uptrend, shares of aTyr Pharma has been making mostly higher lows and higher highs, which is bullish technical price action. This stock has also seen an extreme spike in its upside volume over these last few trading sessions, and it's now quickly moving within range of triggering a near-term breakout trade.

If you're bullish on aTyr Pharma, then I would look for long-biased trades as long as this stock is trending above some its new 52-week low of $3.03 a share and then once it breaks out above some near-term overhead resistance at $4.08 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 325,463 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 $4.39 a share to its 50-day moving average of $4.58 a share, or even $5 to $5.50 a share.

Sears Holdings

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One department stores player that insiders are in love with here is Sears Holdings (SHLD) , which operates as a retailer in the U.S. Insiders are buying this stock into large weakness, since shares have fallen by 41.1% over the last six months.

Sears Holdings has a market cap of $1.5 billion and an enterprise value of $4.5 billion. This stock trades at a fair valuation, with a price-to-sales of 0.06. Its estimated growth rate for this year is -68.6%, and for next year it's pegged at 20.6%. This is not a cash-rich company, since the total cash position on its balance sheet is $238 million and its total debt is $3.14 billion.

The CEO just bought 57,261 shares, or about $821,000 worth of stock, at $14.34 to $14.40 per share.

From a technical perspective, Sears Holdings is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has just started to spike higher right off its 20-day moving average of $14.95 a share. This spike is quickly pushing shares of Sears Holdings within range of triggering a near-term breakout trade above some key overhead resistance levels.

If you're bullish on Sears Holdings then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $14.05 a share and then once it breaks out above some near-term overhead resistance levels at $15.44 to $16.15 a share and then above its 50-day moving average of $16.18 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 671,758 shares. If that breakout hits soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $18 to $18.72, or even $19.50 to its 200-day moving average of $21.03 a share.

Conn's

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Another stock that insiders are in love with here is Conn's (CONN) - Get Report , which operates as a specialty retailer of durable consumer goods and related services in the U.S. Insiders are buying this stock into massive weakness, since shares have dropped sharply by 53.6% over the last six months.

Conn's has a market cap of $345 million and an enterprise value of $1.4 billion. This stock trades at a cheap valuation, with a trailing price-to-earnings of 9.1 and a forward price-to-earnings of 7.3. Its estimated growth rate for this year 14.6%, and for next year it's pegged at 28%. This is not a cash-rich company, since the total cash position on its balance sheet is $109.07 million and its total debt is $1.16 billion.

A beneficial owner just bought 250,000 shares, or about $2.68 million worth of stock, at $10.74 per share.

From a technical perspective, Conn's is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending badly over the last month and change, with shares moving lower off its high of $21.48 a share to its new 52-week low of $10.25 a share. During that downtrend, shares of Conn's have been consistently making lower highs and lower lows, which is bearish technical price action. That said, this stock has now started to rebound off that $10.25 low and it's quickly moving within range of triggering a big breakout trade above some key overhead resistance levels.

If you're in the bull camp on Conn's, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $10.25 a share and then once it breaks out above some near-term overhead resistance levels at $12 to $12.64 a share and then above $13 a share with volume that hits near or above its three-month average action of 1 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 $13.54 a share to its 50-day moving average of $15.18 a share, or even $16 to $17.50 a share.

William Lyon Homes

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One homebuilder that insiders are jumping into here is William Lyon Homes (WLH) - Get Report , which designs, constructs, markets and sells single-family detached and attached homes in California, Arizona, Nevada, Colorado, Washington and Oregon. Insiders are buying this stock into strength, since shares ripped up 27.9% over the last three months.

William Lyon Homes has a market cap of $493 million and an enterprise value of $1.5 billion. This stock trades at a cheap valuation, with a trailing price-to-earnings of 10.5 and a forward price-to-earnings of 5.7. Its estimated growth rate for this year is 35.8%, and for next year it's pegged at 33.3%. This is not a cash-rich company, since the total cash position on its balance sheet is $50.20 million and its total debt is $1.1 billion.

A beneficial owner just bought 172,725 shares, or about $2.46 million worth of stock, at $14.27 per share.

From a technical perspective, William Lyon Homes is currently trending above its 50-day moving average and below its 200-day moving averages, which is neutral trendwise. This stock has been uptrending strong over the last two months and change, with shares ripping higher off its new 52-week low of $7.61 a share to its recent high of $15.80 a share. During that uptrend, this stock has been consistently making higher lows and higher highs, which is bullish technical price action. This strong uptrend has now pushed shares of William Lyon Homes within range of triggering a near-term breakout trade.

If you're bullish on William Lyon Homes, then I would look for long-biased trades as long as this stock is trending above some near-term support at $13.50 a share and then once it breaks out above some near-term overhead resistance levels at $15.80 to $16.76 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 835,995 shares. If that breakout kicks off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $18.09 to its 200-day moving average of $18.17, or even $20 to $22 a share.

vTv Therapeutics

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One biopharmaceutical player that insiders are loading up on here is vTv Therapeutics (VTVT) - Get Report , which discovers, develops and sells orally administered small molecule drug candidates worldwide. Insiders are buying this stock into notable weakness, since shares have dropped by 24.4% over the last six months.

vTv Therapeutics has a market cap of $167 million and an enterprise value of -$50.3 million. This stock trades at a premium valuation, with a price-to-sales of 38.06. Its estimated growth rate for this year is 10.2%, and for next year it's pegged at 25.8%. This is a cash-rich company, since the total cash position on its balance sheet is $97.01 million and its total debt is zero.

A beneficial owner just bought 400,000 shares, or about $2.07 million worth of stock, at $5.20 per share.

From a technical perspective, vTv Therapeutics is currently trending below both its 20-day and 50-day moving averages, which is bearish. This stock has been downtrending badly over the last five months, with shares moving lower off its high of $7.70 a share to its new 52-week low of $4.89 a share. During that downtrend, this stock has been consistently making lower highs and lower lows, which is bearish technical price action.

If you're bullish on vTv Therapeutics, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $4.89 a share and then once it breaks out above some near-term overhead resistance levels at $5.20 to its 20-day moving average of $5.31 a share with volume that hits near or above its three-month average action of 45,274 shares. If that breakout takes hold soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $5.50 to its 50-day moving average of $5.76, or even $6 to $6.20 a share.

Disclosure: This article is commentary by an independent contributor. At the time of publication, the author held a long position in shares of LIFE.