San Francisco-based Fitbit has commercially launched its first wristworn activity and sleep tracking device, Fitbit Flex, which it first announced at the Consumer Electronics Show in January. Fitbit Flex is now on sale for $99.95 at Fitbit.com and at other major retailers, including: Apple Stores, Best Buy, Target, Verizon, and AT&T stores.

While the Flex is the company's first wristorn device -- the others are clip-on smart pedometer form factors -- its also the first tracker from Fitbit to wireless sync with Android and iOS devices via Bluetooth 4.0, according to the company. Samsung Galaxy S III, Samsung Note II, iPhone 4S and 5 users are all able to leverage the Bluetooth 4.0 syncing.

Fitbit confirmed that for NFC-enabled Android devices, Fitbit Flex users can just tap their tracker to their phone and "it will automatically launch your Fitbit stats." Misfit Wearables made a somewhat similar move when it announced that its Shine tracker would handle data uploads through a similar but proprietary mechanism.

The Fitbit Flex also adds a new tracking metric to the mix, too: "active minutes." Like its predecessors the Flex tracks steps taken, distance travelled and calories burned, but its the first device to track active minutes, which Fitbit defines as "moderate-intensity cardio minutes". The CDC recommends the average person gets at least 150 active minutes per week, according to Fitbit.

The Flex is also unique in Fitbit's portfolio of tracking devices for not having a traditional display. Instead it sports a series of five bright white LED lights that indicate how far along a user is to achieving their goals in 20 percent increments.

Like the Fitbit One, the Flex offers a Silent Wake alarm that vibrates the wristworn device at a set time to rouse the wearer, ideally without interrupting their partner's sleep.

The Fitbit Flex sensor can be swapped into a handful of different color wristbands including black, slate, teal, tangerine, and navy blue. While the Flex is sold with black or slate colored bands, accessory packs for teal, tangerine, and navy are available for $14.95 apiece or $29.95 for all three.

Fitbit is facing mounting competition from rival Jawbone, which offers the UP, and recently announced the acquisition of longtime health sensor and activity tracker company BodyMedia. It's also facing a lawsuit from lesser known tracker company Fitbug, which alleges Fitbit copied some of its marketing collateral among other claims. While the reports have not been confirmed by the company, it also supposedly raised $30 million earlier this year at a $300 million valuation.