逆探知[gyakutanchi] phone trace
金属探知機[kinzokutanchiki] metal detector
金探し[kinsagashi] searching for gold
厳探[gentan] strict search
伺い探る[ukagaisaguru] to spy out

私立探偵[shiritsutantei] private detective
手探り[tesaguri] fumbling
人探し[hitosagashi] searching for someone
あら探し[arasagashi] finding fault
探し求める[sagashimotomeru] to search for

窺いしる[ukagaishiru] to perceive
窺う[ukagau] to peep (through)
窺知[kichi] perception

窺い探る[ukagaisaguru] to spy out
窺く[nozoku] to peek (though a keyhole, gap, etc.)
隙を窺う[sukiwoukagau] to watch for an unguarded moment