If the arrest was recent
Start with the county jail
Someone just arrested in Nevada is held in a county or city jail (for example the Clark County Detention Center in Las Vegas, run by LVMPD, or the Washoe County Jail in Reno), not in state prison.
Larger counties post their own online jail/inmate search; smaller ones may not.
If a person is not shown online, call that county/city jail's booking line.
Clark County (LVMPD Detention Center) and Washoe County (Reno) both offer their own online inmate/jail search; smaller Nevada counties may have no online roster. SAVE (save.nv.gov) aggregates custody status for participating Nevada jails and NDOC; call the specific jail if it is not listed.