Proposed is a method for operating a first device (100) in a wireless communication system. The method may comprise the steps of: receiving first SCI for scheduling of a PSSCH, through a PSCCH from a second device; receiving, from the second device through the PSSCH, i) second SCI including a destination L1 ID and a source L1 ID related to the second device and information indicating unicast and ii) a MAC PDU including a DCR message; and determining whether to start an SL DRX inactivity timer, on the basis of a success of decoding the second SCI.