Apple is offering a nice discount on the Apple Watch, but it comes with a catch and is for a limited time only.

Apple will allow customers to purchase an Apple Watch for $50 less than its retail price, as long as they buy it with the new iPhone 6s, CNet reports. 

The promotion from Apple will not be available online and only at certain in-store retailers. The deal can be found at Boston and San Francisco stores, according to an Apple employee in the San Francisco area.

This promotion will only run for a short time, until Nov. 15. It began on Oct. 30, when MacRumors spotted the discount.

The price of the lowest model Apple Watch is the Sport version for $349. This deal would drop that price to $299.

It is unknown how well the Apple Watch has been selling, and Apple is refusing to announce how many units it has sold. The reason the company says they will not disclose this information is because they don't want to tip off their competitors. Analysts polled by Fortune estimate 3.95 million Apple Watch units were sold in the third quarter.

Apple is competing with other smartwatch offerings from companies like Samsung, Motorola and Fitbit. Fitbit sold 4.4 million of their devices in the second quarter.

It is rare for Apple to discount new products like this, so customers might want to jump on the deal as quick as possible. This is a nice way for Apple to encourage people to buy its two latest products -- the Apple Watch and the iPhone 6s. 

It is likely Apple will offer several discounts on its products for Black Friday and the 2015 holiday season, but there is no guarantee the Watch will be included in these promotions. The Apple Watch is expected to be a big seller during the holiday season.