SIsMember

Redix.SIsMember(key, member, callback)

-- Check if player is online
Redix.SIsMember('players:online', playerId, function(err, isOnline)
    if not err and isOnline then
        print('Player is online')
    else
        print('Player is offline')
    end
end)

-- Check permission
Redix.SIsMember('user:permissions', 'admin', function(err, hasAdmin)
    if hasAdmin then
        AllowAdminAction()
    end
end)