USB On-The-Go, often abbreviated to USB OTG or just OTG, is a specification that allows USB devices to act as a host, allowing other USB devices like a USB flash drive, digital camera, mouse, or keyboard to be attached to them. Most newer smartphones support OTG, and if not it can sometimes be enabled by certain software.
Unfortunately, not all devices that support USB OTG provide power to the attached USB devices. Because the Seek Compact imagers are not self-powered, they must be able to draw power from the USB connection.
With all the combinations of device models and software versions, it can be difficult to state with confidence which devices will or won't meet these requirements. If you aren't sure if your device supports USG OTG, you can find some helpful information here.
If you can confirm your device does support USB OTG, you will also need to confirm that it provides power. Unfortunately this is not something that is readily searchable on the web or testable via software. You would have to try connecting a USB device that doesn't have its own power supply and see if it works. Portable USB hard drives are a good thing to test with.
If your phone does not provide power, many people have found success using a cable adapter to attach an external battery pack. This type of connection is not tested by Seek, but here are some examples of the types of adapters and devices customers have tried: