A system comprising a first device, comprising: a first processor for running a first application; a first interface for transmitting and receiving data along a two-way communication channel, and a safety guard consisting of a hardware block between the first processor and the first interface; a second device comprising: a second processor for running a second application; a second interface connected to the second processor for transmitting and receiving data along the two-way communication channel with the first interface; wherein the system is arranged to send safety relevant data from the first application to the second application by: in the safety guard, adding safety information to the safety relevant data to create safety marked data; transmitting the safety marked data through the first interface and the two-way communication channel to the second interface; extracting the safety relevant data from the safety marked data and forwarding the extracted safety relevant data to the second application; retransmitting the safety marked data including the safety information from the second interface back through the two-way communication channel to the first interface as loop back data; in the safety guard, checking the loop back data using the safety information in the loop back data, and if the checking indicates an error, transmitting an error notification signal to the first application and/or the second application. a first device, comprising: a first processor for running a first application; a first interface for transmitting and receiving data along a two-way communication channel, and a safety guard consisting of a hardware block between the first processor and the first interface; a first processor for running a first application; a first interface for transmitting and receiving data along a two-way communication channel, and a safety guard consisting of a hardware block between the first processor and the first interface; a second device comprising: a second processor for running a second application; a second interface connected to the second processor for transmitting and receiving data along the two-way communication channel with the first interface; a second processor for running a second application; a second interface connected to the second processor for transmitting and receiving data along the two-way communication channel with the first interface; wherein the system is arranged to send safety relevant data from the first application to the second application by: in the safety guard, adding safety information to the safety relevant data to create safety marked data; transmitting the safety marked data through the first interface and the two-way communication channel to the second interface; extracting the safety relevant data from the safety marked data and forwarding the extracted safety relevant data to the second application; retransmitting the safety marked data including the safety information from the second interface back through the two-way communication channel to the first interface as loop back data; in the safety guard, checking the loop back data using the safety information in the loop back data, and if the checking indicates an error, transmitting an error notification signal to the first application and/or the second application. in the safety guard, adding safety information to the safety relevant data to create safety marked data; transmitting the safety marked data through the first interface and the two-way communication channel to the second interface; extracting the safety relevant data from the safety marked data and forwarding the extracted safety relevant data to the second application; retransmitting the safety marked data including the safety information from the second interface back through the two-way communication channel to the first interface as loop back data; in the safety guard, checking the loop back data using the safety information in the loop back data, and if the checking indicates an error, transmitting an error notification signal to the first application and/or the second application.