You can try Alarmhandler risk-free for 30 days.  You will then receive an invoice for your first subscription period. If the system was not for you, then just ignore the invoice and your account will be automatically deactivated. Unlike most other services, Alarmhandler does not store your creditcard details upon payment. This means you will never pay for the service, if you do not actively renew it. So to cancel the subscription, just cease to pay the renewal invoices.