Today Ikea announced HomeKit compatibility for their Trådfri line of smart lighting. I assume the bulbs show as accessories in HomeKit but do the motion detectors, dimmers, and switches show up as well?
To see what's currently compatible with HomeKit have a look at HomeKit accessories. The list keeps getting smarter,, at Apple's website.
At the present time, nothing from Ikea is compatible and will not be until later this year in the fall, starting with Ikea's Trådfri line of smart lighting. Explicit compatibility of any other Ikea products has yet to be announced.
Looks like Trådfri lights are HomeKit compatible.
I have a few white GU10 Tradfri lights, a Hue Bridge, and lots of Hue lights. I don't own the Ikea bridge box.
The Tradfri lamps work with the Hue app in iOS, and with Alexa, but I didn't have any luck getting Siri or apple's Home app to recognise them until I ran HomeBridge with the Hue plugin on a Raspberry Pi zero. Now Siri and the Home app see the Tradfri lights and work fine with them.