The most convincing candidate for such a device I've seen is an Illuminati Thumper Pro hidden in Hans's shoe: https://illuminati-magic.com/products/thumper. If you watch the footage of him getting scanned before his match with Alireza (and, crucially, before Magnus announced he was dropping), there are a couple of subtle things that are consistent with this theory: https://www.youtube.com/watch?v=PIulWkTHuu0:
1. He swallows (seemingly nervously) at 4 seconds shortly before his left shoe is scanned.
2. As the left shoe is being scanned, there are 2 beeping noises that at least to me, sound like they are coming from the wand, but are seemingly ignored by the wander. The same beeps do not repeat when his right shoe is scanned (that is, it's not just metal parts built into the shoes themselves). Two caveats to this part: First, I've heard differing opinions on whether the thumper will trigger metal detectors. Second, it's possible (even if unlikely IMO) that those beeps are not from that wand and it's just a coincidence that another wand or object beeped - since we can't see the wand in frame.
3. At 1:17 he starts nervously fidgeting with the credit card as the RF scanner gets close to his left foot and noticeably slows down when the scanner switches from his left foot to the right foot, and appears to stop completely as soon as the scanner is moving up away from his right foot. The RF scanner, to my understanding, would only detect devices that are actively transmitting which the thumper shouldn't need to do at all if Hans were using purely to receive engine moves/hints during the but the fact that it theoretically could transmit would explain why he'd be nervous about getting scanned anyway.
Of course none of these observations are proof but they sure look suspicious to me.
