Hi,
You’re going to have to be more specific as IKEA sells many devices branded TRÅDFRI from motion sensors to multi-button remotes.
Which sensor? Sensing what? Product / model code? Web link to the catalogue?
Why not?
You need to help us help you by describing your environment in enough detail so we can understand it.
You don’t need the IKEA hub (neither of the at least two versions), but you do need a Zigbee co-ordinator radio like the SkyConnect or one of the similar Sonoff USBdevices.
There are several IKEA devices that need an extra component to decode the non-standard IKEA implementation of Zigbee - e.g the Rodret two button remote.
IKEA produces good quality hardware cheaply with stores world wide. They don’t fully match standards, but there’s enough HASS users out there to fix their meddling in code.
If this helps, 
this post!