This is a prototype for a PowerShell script that monitors the status of each component of Search Service Application in SharePoint 2013. This script can be saved  to a .ps1 file and run by the Window Task scheduler periodically. If it detects that any of the component is not in the “Active” state, it automatically sends an email to the administrator.

Add-PSSnapin Microsoft.SharePoint.PowerShell
#Declare variables for later use.
$ssa = Get-SPEnterpriseSearchServiceApplication
$status = Get-SPEnterpriseSearchStatus -SearchApplication $ssa
#Create an empty array to store any component that is not active.
$unhealthy = @()
#Loop through each component status, and store any one that is not active to the array.
$number = 0
$status | foreach {
if ($_.state -ne "active"){
$number++
$unhealthy +=$number.ToString() + ". " + $_.name + "`n"
}
}

#If there is any component that is not active, send an email to the admin with the component name in the email body.
if ($unhealthy.count -gt 0) {
$result = "The components below are not active:`n " + $unhealthy
$params = @{'To'='whomitmayconcern@company.com'
'From'='admin@company.com'
'Subject'='Attention! Search Service Components Unhealthy'
'Body'=$result
'SMTPServer'='smtp.contoso.com'}
Send-MailMessage @params
}

The script has been tested with a single server farm with a single Search Service Application. If your scenario is different, you should adjust the script accordingly.