SentryKit allows you to track up to 8 primary keywords search ranks for any ASIN you are tracking.
You can add the keyword by opening the ASIN main page.
When adding the keyword, you can also specify to be alerted if the rank falls below the value you set. For no alerts, just leave the rank blank.
Get alerted when you are above the rank value.
To get alerted when your keyword keyword rank reaches a specific rank/threshold, Simply turn on the "Improvement" checkbox for the Keyword Alerts in your email settings.
If you start below that threshold then later you meet the threshold you will get a notification about it.