Bindwise Monitoring & Alerts is free as long as you want.
Free Bindwise plan offers all the functionality limited to a monthly tracking duration.
Monitoring runs 7 days/mo. Unfortunately, you can't choose these 7 days. After a 30-day free trial, you'll have no service for 23 continuous days, then tracking will be enabled for 7 continuous days. And so on.
Alerts for those 23 inactive days are deleted.
During the 7 days of active monitoring on a free plan, you'll be able to receive up to 50 alerts/day.