In telecommunication, the term start signal has the following meanings: 1. * A signal that prepares a device to receive data or to perform a function. Contrast with A-condition. 2. * In asynchronous serial communication, a signal at the beginning of a character that prepares the receiving device for the reception of the code elements. A start signal is limited to one signal element usually having the duration of a unit interval. Source: from Federal Standard 1037C and from MIL-STD-188