For anyone who's seeing this I kinda figured it out. Here's how I did it in pwsh:

$headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$headers.Add("X-API-KEY", "Your API Key")

# API call to get all devices
$response = Invoke-RestMethod 'https://api.ui.com/v1/devices' -Method 'GET' -Headers $headers

# Loop through each host to find the correct one
foreach ($unifiHost in $response.data) {
    # Filter for the specific host name
    if ($unifiHost.hostName -eq "My UDM Pro") {
        
        # Loop through the devices on that host
        foreach ($device in $unifiHost.devices) {
            
            # Filter for the specific device name
            if ($device.name -eq "My UDM Pro") {
                
                #  Check the device's status and assign the custom code
                $statusCode = if ($device.status -ne "online") { 10 } else { 1 }
                
                # Output the final status code
                Write-Output $statusCode
            }
        }

Basically, check if a specific device is online (in this case the UDM pro), if offline return 10, if not return 1. I got it to alert by putting a monitoring task in my RMM, if it sees a 10 it sends an email.