PowerShell script checks for available updates and returns the result in the standard monitoring plugin output format.

check_updates.ps1

$Session = New-Object -ComObject "Microsoft.Update.Session"
$Searcher = $Session.CreateUpdateSearcher()
$Result = $Searcher.Search("IsInstalled = 0 and IsHidden = 0")
$Updates = $Result.Updates

$Total = $Updates.Count
$Critical = @($Updates | Where-Object {$_.MsrcSeverity -eq 'Important' -or $_.MsrcSeverity -eq 'Critical'}).Count

if ($Critical -gt 0) {
	$CheckResult = 'CRITICAL'
	$ExitCode = 2
}
elseif ($Total -gt 0 ) {
	$CheckResult = 'WARNING'
	$ExitCode = 1
}
else {
	$CheckResult = 'OK'
	$ExitCode = 0
}

Write-Output "$($CheckResult): $($Total) updates available ($($Critical) critical updates)."
Exit $ExitCode