How can I turn off auto-discovery?

Is it possible disable the auto-discovery? The auto-discovery added devices and sensors I do not want to monitor. How can I configure PRTG so that these devices are not added?

Automatic auto-discovery is set on group or device level. You can change it in your group's or device's settings, section Group Type or Device Type, setting Sensor Management.

The easiest way to disable auto-discovery for all devices is to use multi-edit: From the main menu in the PRTG web interface, select Devices | Device List, select all of your devices and click the settings symbol. You can then change Automatic device identification under Sensor Management for all devices simultaneously and click OK to save your settings.

As of PRTG version 21.2.67, the initial Auto-Discovery can be disabled by using the "Custom" Installation Mode during the installation process. For older PRTG versions, you can disable the initial auto-discovery for a fresh PRTG installation by running the installer in command prompt and adding /NoInitialAutoDisco=1 as parameter. 

Tip:  You can monitor the config file for devices / groups with an enabled auto discovery:

[string] $ConfigurationFilePath = ((Get-ItemProperty -Path "hklm:SOFTWARE\Wow6432Node\Paessler\PRTG Network Monitor\Server\Core" -Name "Datapath").DataPath) + "PRTG Configuration.dat"
   [xml] $configuration = New-Object -TypeName XML;
         $configuration.Load($ConfigurationFilePath)

[System.Collections.ArrayList]$ADEnabledGroups = @();
[System.Collections.ArrayList]$ADEnabledDevices  = @();

$Groups = ($configuration.SelectNodes("//group"))
$Devices = ($configuration.SelectNodes("//device"))

foreach($Device in $Devices){
    if($device.data.discoverytype.trim() -ne 0)
    { $ADEnabledDevices.Add($device.id); }
}

foreach($Group in $Groups){
    if($group.data.discoverytype.trim() -ne 0)
    { $ADEnabledGroups.Add($group.id); }
}

if($ADEnabledDevices.Count -eq 0)
{ $DeviceMsg = "No devices with AutoDiscovery found." }
else
{ $DeviceMsg = [string]::Format("Devices with AutoDiscovery found: {0} ({1})",$ADEnabledDevices.Count,$ADEnabledDevices -join ", ") }

if($ADEnabledGroups.Count -eq 0)
{ $GroupMsg = "No groups with AutoDiscovery found." }
else
{ $GroupMsg = [string]::Format("Groups with AutoDiscovery found: {0} ({1})",$ADEnabledGroups.Count,$ADEnabledGroups -join ", ") }

$Msg = [string]::Format("{0} | {1}",$GroupMsg,$DeviceMsg);
$Count = $ADEnabledGroups.Count + $ADEnabledDevices.Count;

Write-Host ([string]::Format("{0}:{1}",$Count,$Msg))

Note
Since the script checks the configuration, it will take 10 minutes until a configuration change (i.e. an activated auto discovery) will be noticed.

Note that you need to set a limit, preferably to an upper error limit of 0. Save it to <PRTG>/Custom Sensors/EXE/find-autodiscoveries.ps1 and create a new EXE/Script sensor. Select the script and it should run. Will look somewhat like this:

Disclaimer:
The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.