Voice notifications and signal tones for common use in a room or outdoors 8 different signal tone inputs (stage) Micro SD memory card Common signal tone volume on a 4 GB memory card: about 108dB (A) for 230 V AC or 24 VDC EV 21 Voice speakers are electronic signaling devices for indoor and outdoor use. When a 230 VAC or 24 VDC supply voltage is applied, the device emits various warning tones and plain text announcements. Plain text announcements are clearer than warning sounds because announcements require direct action, whereas warning sounds must be interpreted.