My Mac is Beeping, what does that mean?

Picture this. You just arrived home from work. You power on your iMac, and you hear three beeps, a five-second pause, then the same three beeps again. What does that mean? Well it means in nice terms, your RAM is malfunctioning.

For Macs with an LED light predating 2008, they do not beep, but rather the LED flashes. Here are the current flashing combinations:

Non-stop LED blinking: No RAM detected

Three LED Blinks, 5 second pause, repeat: Bad RAM

SOS LED blinking (blinks nine times): This will only happen if you set the Mac into EFI flashing mode, and the PEI (Pre-EFI Initialisation detects the Mac EFI is corrupt and enters firmware recovery mode.

For Macs 2008 onwards and the iMac (Mid 2007) up to early 2013:

One singular beep: No RAM detected

Three beeps: Bad RAM

Nine beeps: SOS Mode, will attempt to recover the EFI from a previously saved image.

One long beep: EFI is about to be set to read-write mode.

For Macs Mid 2013 onwards without a T2 chip:

One singular beep: No RAM

Three beeps: Bad RAM

Nine beeps: EFI recovery mode (pre-2016 devices)

For Macs with a T2 chip, they do not produce beeping sounds.