A method and control arrangement to secure an alarm system in a site to be monitored. The readiness to forward an alarm out of the site is monitored with a control arrangement through which at least data transmission connections of the alarm system to outside the site are repetitively checked to enable sending the alarm via at least one secondary alarm connection in case the primary alarm connection is prevented. The control arrangement includes at least two controlling devices that monitor continuously the electric connection/readiness of the site to at least two of the following: a data transmission route working on a free frequency, a mobile phone network, an electricity grid, the internet, one or several other controlling devices, a communication connection working on a free frequency, an alarm arrangement belonging to the alarm system, a wired connection.