How To Monitor If My Website Is Up
It can send you emails when you site goes down and will email again to say when everything is ok. The check interval for the free plan is only 30 though so is not hugely accurate for this plan but still you can be advised when it happens so you can give your website host some grief!!
I could save you some money as well if you are using adwords for example and your website goes down it would be best to turn it off while it is. Saving for spending money for clicks that go no where.
Also gives you an idea of how well your host is doing and if it keeps happening to purhaps looking at getting a new one or to put in place a service where you can divert it when it goes down to a backup host.