Energy efficiency is essential when developing IoT devices. Test equipment for energy consumption is complex, costly and accessible only to a small number of hardware specialists, making testing a time-consuming development step for most companies.
The expected battery life of IoT products depends on battery capacity and hardware setup, but also to a large extent on system behavior. In order to verify expected battery life, testing must be carried out on a live system. Testing should be minimally invasive, and correctly capture and present how the system behaves during a representative time period.
This case study outlines the results of Strips by Sensitive battery life tested using the Otii system by Qoitech – an easy-to-use, affordable tool for energy optimization in apps and IoT devices.
Strips, developed and marketed by Sensative AB, are wireless magnetic sensors that invisibly mount on windows and doors to indicate if they are open or closed. They are battery powered and communicate using the Z-Wave network protocol.
Two separate measuring sessions were carried out with the Strips units in the environment shown below; one with direct communication between the Strips and the gateway, and one session with communications via a Z-Wave extender.
Both sessions include simulating 12 open and 12 close events during the 24-hour measuring period. These events will each trigger a radio transmission. All Z-Wave devices will additionally report their status periodically. In the case of Strips, the default is every 24 hours.
Using the Otii system makes measuring even a very dynamic system such as Strips by Sensative easy and straightforward. The low quiescent current between active periods can easily be measured, and selecting a region in the graph will instantly show the detail and amount of energy consumed within it.
With the Otii system, we have been able to confirm that under the given assumptions Strips have a battery life of 10 years or even more in typical Z-Wave network.
However, as can also be seen using the Otii system, communication between wireless devices in a large network environment is complex, and low signal strength, or repeaters, would have an impact on battery performance.