10 things you need to know before the opening bell

Reuters/Lisi Niesner

Bulgaria's Vladimir Zografski in action during training.

Here is what you need to know.

1. Apple warns China is slowing down. CEO Tim Cook sent a letter to investors on Wednesday that cut Apple's first-quarter guidance, citing a slowdown in China's economy.
2. Major Apple suppliers are getting pounded. The facial-recognition sensor-maker AMS plunged as much as 17% Thursday while chipmaker Dialog Semiconductor shed 8%.
3. Stocks are under pressure. Apple slid 8% in after-hours trading, taking down other tech names with it. The S&P 500 was set to open lower by 1.65% after China's Shenzen Composite fell 0.8% and the Euro Stoxx 50 was down 1.08%.
4. A 'flash crash' ripped through Asia's currency market. The Japanese yen soared versus its peers late Wednesday, gaining as much as 3.7% versus the US dollar and 7.2% versus the Australian dollar as moves were exacerbated by thin holiday volumes.
5. 3 top-ranked investment pros all like the same overlooked corner of the market. They all think cellular towers are going to yield big returns in the year ahead - here's which names they like and why.
6. Here's how we'll know when the stock market's bottom is in. "To confirm the resumption of a new bull market we'd like to see this internal breadth gauge surge to 70% like it did at the start of new bulls in 1994, 2003, 2009, 2013, and 2016," Ari Wald, Oppenheimer's head of technical analysis, wrote in a note on Tuesday.
7. Tesla sinks after missing on deliveries and cutting prices. Shares fell 6.81% Wednesday after the electric-car maker announced fourth-quarter Model 3 deliveries and full-year Model S and Model X deliveries that missed expectations and the company said it was lowering prices on the three models by $2,000 each.
8. GE started off the new year with a bang. General Electric shares surged 6.21% Wednesday - if the gains hold up all year it would be the best annual performance for the industrial conglomerate since 2015.
9. The value of a typical Manhattan apartment just fell below $1 million. The median sales price of units sold in Manhattan fell almost 6% to $999,000 from October to December, making for the lowest reading in three years, according to a report from listing broker Douglas Elliman Real Estate.
10. US economic data is heavy. ADP Employment Change will cross the wires at 8:15 a.m. ET before initial claims is released at 8:30 a.m. ET. Then, at 10 a.m. ET, ISM Manufacturing is due out. US auto sales will be announced throughout the day. The US 10-year yield is up 2 basis points at 2.64%.