Will only pass down the pipeline if the object, or object property has changed from the previous value. Useful for monitoring the status of a system.

Select-OnChange.ps1

function Select-OnChange {
param(
    [Parameter(Mandatory, ValueFromPipeline)]
    $InputObject,

    [Parameter()]
    $PropertyName
)

PROCESS {
    if ($PSBoundParameters.ContainsKey('PropertyName')) {
        if ($LastValue.$PropertyName -ne $InputObject.$PropertyName) {
            Write-Output $InputObject
        }
    }
    else {
        if ($LastValue -ne $InputObject) {
            Write-Output $InputObject
        }
    }
    $LastValue = $InputObject
}
}