A method for fire alarm by using an air conditioner , comprising: detecting (S101) smoke concentration in a space where an indoor unit of the air conditioner is located; when a second specified condition is satisfied, controlling the air conditioner to start a second mode to perform an alarm prompt; and when a first specified condition is satisfied, controlling the air conditioner to start a first mode to perform a warning wherein the controlling the air conditioner to start the first mode to perform the warning comprises: activating (S103) a first alarm sound mode and sending (S104) warning information to a server, so that the server forwards (S105) the warning information to a terminal device of a user. wherein the controlling the air conditioner to start the second mode to perform the alarm prompt comprises: activating (S107) a second alarm sound mode and sending (S108) alarm prompt information to a server, so that the server forwards (S109) the alarm prompt information to a terminal device of a user to prompt the user to perform a fire alarm; wherein the alarm prompt information comprises smoke concentration information, or smoke concentration information and alarm mode information. detecting (S101) smoke concentration in a space where an indoor unit of the air conditioner is located; when a second specified condition is satisfied, controlling the air conditioner to start a second mode to perform an alarm prompt; and when a first specified condition is satisfied, controlling the air conditioner to start a first mode to perform a warning wherein the controlling the air conditioner to start the first mode to perform the warning comprises: activating (S103) a first alarm sound mode and sending (S104) warning information to a server, so that the server forwards (S105) the warning information to a terminal device of a user. wherein the controlling the air conditioner to start the second mode to perform the alarm prompt comprises: activating (S107) a second alarm sound mode and sending (S108) alarm prompt information to a server, so that the server forwards (S109) the alarm prompt information to a terminal device of a user to prompt the user to perform a fire alarm; wherein the alarm prompt information comprises smoke concentration information, or smoke concentration information and alarm mode information. activating (S103) a first alarm sound mode and sending (S104) warning information to a server, so that the server forwards (S105) the warning information to a terminal device of a user. wherein the controlling the air conditioner to start the second mode to perform the alarm prompt comprises: activating (S107) a second alarm sound mode and sending (S108) alarm prompt information to a server, so that the server forwards (S109) the alarm prompt information to a terminal device of a user to prompt the user to perform a fire alarm; wherein the alarm prompt information comprises smoke concentration information, or smoke concentration information and alarm mode information. activating (S107) a second alarm sound mode and sending (S108) alarm prompt information to a server, so that the server forwards (S109) the alarm prompt information to a terminal device of a user to prompt the user to perform a fire alarm; wherein the alarm prompt information comprises smoke concentration information, or smoke concentration information and alarm mode information. <EOS>