9. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving, by a computing device, audio data that corresponds to an utterance; determining that the utterance likely includes a particular, predefined hotword; in response to determining that the utterance likely includes the particular, predefined hotword, determining score that reflects a loudness of the audio data; determining a duration of a delay period, wherein the duration of the delay period is inversely proportional to the loudness of the audio data; activating a mode in which the computing device temporarily listens, for the duration of the delay period, for a predetermined audio signal that indicates that another computing device is commencing speech recognition processing on the audio data; after the duration of the delay period has elapsed without hearing the predetermined audio signal from another computing device, deactivating the mode and transmitting the predetermined audio signal that indicates that the computing device is commencing speech recognition processing on the audio data; and after transmitting the predetermined audio signal, processing at least a portion of the audio data using an automated speech recognizer on the computing device.
9. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving, by a computing device, audio data that corresponds to an utterance; determining that the utterance likely includes a particular, predefined hotword; in response to determining that the utterance likely includes the particular, predefined hotword, determining score that reflects a loudness of the audio data; determining a duration of a delay period, wherein the duration of the delay period is inversely proportional to the loudness of the audio data; activating a mode in which the computing device temporarily listens, for the duration of the delay period, for a predetermined audio signal that indicates that another computing device is commencing speech recognition processing on the audio data; after the duration of the delay period has elapsed without hearing the predetermined audio signal from another computing device, deactivating the mode and transmitting the predetermined audio signal that indicates that the computing device is commencing speech recognition processing on the audio data; and after transmitting the predetermined audio signal, processing at least a portion of the audio data using an automated speech recognizer on the computing device. 12. The system of claim 9 , wherein the predetermined audio signal comprises an ultrasonic signal.