Laravel - How to check which column is updated using Observers

I want to know about only one column which is bieng updated using observer

<?php


namespace App\Observers;


use App\OnsiteHistory;

class OnsiteHistoryObserver
{

    public function updated(OnsiteHistory $onsiteHistory)
    {
        if ($onsiteHistory && strtolower($onsiteHistory->status) == 'accepted'){

           // send email  

        }
    }
}

I want to check only status column is updated. How do I can do that?

via Chebli Mohamed