How can you get the battery to last that long?
Several technical solutions have been used to ensure long battery life. Currently we do not have an accurate estimated of the battery life, but we are aiming at 9-12 months.
- The radio uses Bluetooth Low Energy, and as the name dictates the radio uses very little power.
- Furthermore, we use the absolute minimum transmission power, also to avoid false positives. That means our radios are out of reach after single digit meters.
- We also use a movement sensor to see if the tag is in use or not. The sensor shows movement in X, Y and Z direction, and will show 1g (earth’s gravity) in the Y direction when the sensor is worn in a lanyard or on a clip-on, and in the Y and X direction if the clip-on is worn in a shirt pocket. But it will show 1g in the Z-direction if the token is laying down. Furthermore, the movement sensor can also tell if the token is actually moving. Using this information, we simply turn off the token when it is not in use.
- Because the contact event has to last minimum 15 minutes, our tokens wakes up for a few seconds every 5 minutes. They scan for other tokens, record events and goes back to sleep. The 5 minutes are controlled so all tokens wake up exactly at the same time. Because of this technique the tokens are asleep 98.5% of the time and use minimal power in that time.
- The tokens uses WiFi to upload the contact events. This happens every 5-7 hours, when the token is in use. The time frame is random, not to overload the WiFi at one specific time. The upload takes a few seconds and contains a compact form of the contact event information which is transmitted using an SSL (HTTPS) connection to our backend servers located at Amazon Web Services (AWS) in Cape Town, South Africa.
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