The future of Apple Watch will identify users through heartbeat
Mobile devices (and wearable devices) are obvious biosecurity measures. Whether it looks like a forced RFID or NFC implant, or multiple standards like retina scans and fingerprint sensors, security exceeds common passwords now. Apple Watch is not immune to this progress. Antimony Trioxide Flame Retardant,Environmentally Friendly Antimony Trioxide,Nano Scale Antimony Trioxide,Nano Scale Antimony Trioxide HUNAN ZHONGNAN ANTIMONY&TUNGSTEN TRADING CO.,LTD , https://www.znat.com.cn
In a patent application published today, Apple details the method that will measure the oxygen content in blood. We don't have the details of the patent yet. It is at least the company's interest in exploring. In fact, Apple may already be interested in technology. The first generation of Apple Watch was determined to contain the necessary hardware but never activated. 
According to the contents of the file:
The light emitters and light sensors can be used to perform biometric recognition based on recognition of the user's blood vessel characteristics for the user. For example, light information may be obtained at one or more light sensors and the information may be compared to stored information associated with the user's identity. Based on this comparison, the user of the device can be identified as having the user's identity.
If the company chooses to include the technology from the patent application, future models can create unique markers for using the heartbeat as the wearer.