I think, Aditya is FINALLY starting to trust Samaira! He doesn't suspect her to be Shikha anymore (which is GREAT)! Samaira has not given him ANY reason to doubt her- so why would he fix a microphone in there? That's why I think it's just an extremely expensive watch!
Also, if it was a microphone and he ends up knowing she's Shikha, we'll be back to square one. Where would the story go after that? Would she undergo another makeover? How would she get back at him ever again?
So, IMO it's just a gift since he refused the coffee, and somewhere he's beginning to like her! 😉