there is a difference of opinion on the permissibility of wristwatches with metalic chain. 'huzur mufti-e-azam hind 'hazrat molana Mustafa Ridha Khan 'alaihi rah'ma wa ridhwan opined, even after some scholars argued with him quite at lenght, that it was impermissible, whereas 'hazrat allama moalana sharif al-haq amjadi was of the view that it was legitimate. many of our contemporary ulama too do not allow it, among them are 'hazrat allama molana akhtar ridha khan, 'hazrat molana abdul 'hakeem sharaf qadri,'hazrta molana shah turab al-haq qadri and many others (may Allah save them), whereas i've seen several other ulama wearing such wristwaches. i conjecture that to be on the safe side and specially to avoid difference of opinion, those who wear such wristwaches should remove them while praying, though prayer would be valid according to the ulama who allow it.