Waters Lots of selling was also seen by three key corporate insiders at Waters, one of TheStreet Ratings' top-rated life sciences stocks. This is an analytical instrument manufacturer. This stock has done well so far in 2011 with shares up over 25%, but there could be some downside in store now for this name. The CFO, vice president of human resources and general counsel combined to sell over 278,506 shares, or $27.3 million worth of stock at an average price of $98.04. The CFO made up the bulk of the selling after options were exercised to the tune of over $17 million. CFOs understand the most about how any company is performing from financial perspective, and this large selling by Waters' CFO could be an early warning sign From a technical standpoint, I don't like that Waters has recently put in a double-top chart pattern at around $100 a share. This stock has a huge gap that could get filled to the downside that would take shares toward $90. There are even some gaps below $90 that could get filled taking WAT all the way down to a notable support level at around $85 a share. I would only be a buyer of this stock in the short term if it broke the double-top chart pattern and moved above $100 on heavy volume well above the three-month average of 705,000 shares. One could short this stock soon with a stop above $100 and add heavily to the position if Waters takes out $95.50, since that will put the big gap down in price into play quickly. Equity Residential Another stock with heavy insider selling that could be forming a double-top chart pattern is real estate investment trust Equity Residential, which is focused on the acquisition, development and management of apartment properties in U.S. markets. So far in 2011, this stock has trended higher by over 14%. That said, the recent heavy selling combined with a troubling near-term chart pattern could mean Equity Residential is setting up to head much lower. A number of key insiders at Equity Residential have been dumping a ton of stock recently. That list includes the president and CEO, general counsel, CFO, CIO and a number of directors. Most of the selling was the exercising of options that combined to total 412,812 shares, or $24.6 million worth of stock at an average price of $59.60. From a technical standpoint, Equity Residential is starting to find some heavy resistance at around $60 a share. The stock has tested this level about six times in the past few weeks and has been unable to trade above it. Another early warning sign of a potential double chart here with Equity Residential at $60 is the declining up volume during the past couple of weeks. One could short this stock with a stop above $60 and add heavily to the position if it falls below near-term support at around $58.34 a share. A downside target of $56.50 to $55 a share could be achieved very quickly if Equity Residential is indeed putting in a double top. A big bullish bet on Equity Residential comes from Ken Heebner's Capital Growth Management, which reported a 1.6 million-share position in the stock as of the most recent period. To see more stocks with notable insider activity such as Baker Hughes ( BHI), Johnson & Johnson ( JNJ) and St. Jude Medical ( STJ), check out the Stocks With Notable Insider Activity portfolio on Stockpickr. -- Written by Roberto Pedone in Winderemere, Fla.