Set stop price and add-position price according to the cost and current ATR.
You may set an alert with the condition when the stock price crossing down the Stop Price.
Example:
stock price: $150
volatility multiple: 2
current ATR: $3
stop price = $150 - $3 * 2 = $144
add-position price = $150 + $3 * 2 / 2 = $153
