Cash! Holding cash waiting for an entry is essentially a synthetic put/short position since you are making money as the stock drops...but it carries no risk to capital...no fees, no commission, no time decay.
But you are making profits as the price drops... Because the more it drops, the more shares you're going to be able to purchase. It's exactly the same as holding a short position... Without any upside risk. I call it the Phantom short.
I think you edited your post. The way it was worded made it sound like just sit on the sideline and dont do anything period.
Technically you can and it will perform the same as holding a short position minus the upside risk. Example: You wish to buy 100k worth of abc stock trading at $10. You could by 10,000 shares. If price drops to $8 you can now buy 10,000 shares with only $80,000. You have just (phantom) profited 20k Short 10,000 shares @ $10 and price drops to $8 you profit 20k.
Well I'm glad you have a working crystal ball that guarantees price will keep moving in the direction you hoped.
Seem to me that there is no "zero risk" way to make ANY play in the markets. There are some "low risk, low profit potential" plays... buy none are zero risk.