A safety input device (502; 1002b) for use on a single-wire safety circuit, the safety input device comprising: a memory that stores computer-executable components; a processor, operatively coupled to the memory, that executes the computer-executable components, the computer-executable components comprising: a safe state detection component configured to determine whether the safety input device is in a safe state; a pulse detection component configured to verify that a modulated pulse pattern of a safety signal received on an input terminal of the safety input device corresponds to a defined pulse pattern; a safety signal relaying component configured to output the safety signal on an output terminal of the safety input device in response to verification that the modulated pulse pattern corresponds to the defined pulse pattern and a determination that a safety function of the safety input device is valid; and a message processing component configured to process a first input message received via the input terminal, to process a second input message received via the output terminal, to send a first output message via the input terminal, and to send a second output message via the output terminal; wherein the second input message received via the output terminal is an enumeration message containing an address of a downstream safety device, wherein the safety input device further comprises a device addressing component configured to, in response to receipt of the second input message, increment the address to yield an incremented address and assign the incremented address to the safety input device, and wherein the second output message comprises an enumeration response message containing at least the incremented address, an indication of whether the safety input device is a last addressable device on a safety circuit, and an indication of whether the safety input device is operating in the safety master mode. a memory that stores computer-executable components; a processor, operatively coupled to the memory, that executes the computer-executable components, the computer-executable components comprising: a safe state detection component configured to determine whether the safety input device is in a safe state; a pulse detection component configured to verify that a modulated pulse pattern of a safety signal received on an input terminal of the safety input device corresponds to a defined pulse pattern; a safety signal relaying component configured to output the safety signal on an output terminal of the safety input device in response to verification that the modulated pulse pattern corresponds to the defined pulse pattern and a determination that a safety function of the safety input device is valid; and a message processing component configured to process a first input message received via the input terminal, to process a second input message received via the output terminal, to send a first output message via the input terminal, and to send a second output message via the output terminal; wherein the second input message received via the output terminal is an enumeration message containing an address of a downstream safety device, wherein the safety input device further comprises a device addressing component configured to, in response to receipt of the second input message, increment the address to yield an incremented address and assign the incremented address to the safety input device, and wherein the second output message comprises an enumeration response message containing at least the incremented address, an indication of whether the safety input device is a last addressable device on a safety circuit, and an indication of whether the safety input device is operating in the safety master mode. a safe state detection component configured to determine whether the safety input device is in a safe state; a pulse detection component configured to verify that a modulated pulse pattern of a safety signal received on an input terminal of the safety input device corresponds to a defined pulse pattern; a safety signal relaying component configured to output the safety signal on an output terminal of the safety input device in response to verification that the modulated pulse pattern corresponds to the defined pulse pattern and a determination that a safety function of the safety input device is valid; and a message processing component configured to process a first input message received via the input terminal, to process a second input message received via the output terminal, to send a first output message via the input terminal, and to send a second output message via the output terminal; wherein the second input message received via the output terminal is an enumeration message containing an address of a downstream safety device, wherein the safety input device further comprises a device addressing component configured to, in response to receipt of the second input message, increment the address to yield an incremented address and assign the incremented address to the safety input device, and wherein the second output message comprises an enumeration response message containing at least the incremented address, an indication of whether the safety input device is a last addressable device on a safety circuit, and an indication of whether the safety input device is operating in the safety master mode.