October is shaping up to be the least volatile month for equity markets in modern history.

That's what technician Carley Garner told Jim Cramer during the Off the Charts segment on Mad Money Tuesday. Garner is a contributor to Real Money and will be doing a teach-in with Cramer on Saturday at the Harvard Club, in New York.

Garner says the calm in the markets is unprecedented. Stocks have now had the longest streak without a 3% pullback since before the Great Depression -- 242 days without a substantial decline. In addition, the S&P 500 is close to breaking the record for most consecutive sessions without a 1% intraday move.

Against a backdrop of earnings growth coupled with an accelerating economy in the U.S. and abroad, the healthy bull market makes sense.

But Garner is worried because historically, periods of minimal volatility lead inexorably to periods of surging volatility, and when that happens stocks tend to sell off. Calmness breeds complacency, according to Garner, and sooner or later complacency gets punished.

To get a better handle on these issues, Garner and Cramer looked at a chart of the implied volatility in the NASDAQ 100, the tech-heavy index that includes the 100 largest non-financial stocks in the Nasdaq  Composite. (Implied volatility measures the level of uncertainty traders are baking into option prices. The less people pay for options, the less likely the markets are to behave wildly.)

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Garner points out that its implied volatility is approaching 12%, only the fourth time it's gotten this low in the past decade. In other words, there's an extreme lack of fear in the NASDAQ 100.

But it's even more extreme in the S&P 500. At the moment, the S&P futures are carrying an implied volatility of less than 8% -- an all-time low.

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Garner finds it hard to imagine how this market could become less volatile. But she thinks it can easily get more volatile, and when that happens, there's a decent chance of a pullback.

Currency is also at play in the market surge. Earlier this year the dollar fell sharply against major currencies, instantly making U.S. multinational companies more profitable. That's been a boon for the market. As Garner points out, the S&P futures have a negative 86% correlation with the greenback, meaning as the dollar goes down, stocks go up -- and vice versa.

The problem now is that there's a strong seasonal pattern in the US Dollar Index. Over the past five years, the dollar's had a strong tendency to rally in late October and early November. And if that pattern plays out again this year, it could be bad news for both the S&P and the NASDAQ.

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As for the actual index charts, they look great for the past year. Ever since the election, both averages have rocketed higher -- the S&P gaining 25% and the NASDAQ 100 up 29%. But Garner's concerned that the run in the Nasdaq relies too heavily on a small number of red-hot stocks that make up the so-called FANG group of Facebook (FB) - Get Report , Amazon (AMZN) - Get Report , Apple (AAPL) - Get Report , Netflix (NFLX) - Get Report and Alphabet (Google) (GOOGL) - Get Report . If any of them falter, the broader market could turn down quickly.

The monthly chart of the S&P 500 is also a cause for concern, according to Garner. She notes that the Relative Strength Index, or RSI -- an important momentum indicator -- has reached 80 for the first time since 1997. A reading over 70 is rare and signals that an overbought position.

Over the past 20 years, the RSI on the S&P 500's monthly chart has broken out above 70 three times: at the peak of the dot-com bubble in 1999 and 2000, then right before the financial crisis in 2007, and then the oil implosion in late 2014.

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Garner also thinks the S&P's trajectory is too steep. It's coming very close to its long-term ceiling of resistance formed by the trendline, currently at 2,600.

This ceiling has held firm since the bottom in 2009 and Garner expects it will continue to hold. The S&P could plunge roughly 17% to the mid 2100s before it runs into its long-term floor of support.

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The NASDAQ 100's monthly chart also reflects similarly overbought conditions. The Nasdaq's relative strength index is at 77. And, like the S&P, the NASDAQ 100 is very close to its ceiling of resistance and a long way away from its floor of support -- it could fall 18% and still be within its long-term uptrend.

Join Jim Cramer, Carley Garner and Other Experts Oct. 28 in New York

Jim Cramer will host Carley Garner, CNBC's Jon Najarian, TD Ameritrade's JJ Kinahan, and other market mavens on Oct. 28 in New York City to share successful strategies for active investors. 

You can join them as they discuss how smart investors can make the most of options trading, futures contracts, fundamental and quantitative analysis and great ETFs to buy right now. Participants will also get a chance to meet Jim and other panelists and take photos.

When: Saturday, Oct. 28, 8 a.m.-3 p.m. 

Where: The Harvard Club of New York, 35 West 44th St., New York, N.Y.

Cost: $250per person. 

Click herefor the full conference agenda or to reserve your seat now.

On Real Money, Cramer says if you ask him, some of these tech companies are begging to be acquired. And it would be great if they were. Get more on his insights with a free trial subscription to Real Money.

Cramer and the AAP team are trimming some of their Cimarex (XEC) - Get Report shares to increase flexibility in both the portfolio and in their position. Find out what they're telling their investment club members and get in on the conversation with a free trial subscription to Action Alerts PLUS.

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