I'd like a debian laptop with LXDE to do a system beep every 10 or 30 seconds once the battery reaches a critical level. is that possible?
Yes, it is possible. One way is listening for udev events when the battery level changes, and comparing it against a threshold. Otherwise, this is a quick and dirty way. Make a systemd service to start this in the background at boot and you'll get beeps every 10 seconds once your battery level drops below 5%.
#!/bin/bash let CRIT_BATT_LVL=5 let PERIOD=10 exec 3>&2 exec 2>/dev/null while true; do level=$(acpi -b | grep -oP '\d+(?=%)') if [ $level -lt $CRIT_BATT_LVL ]; then timeout -k 0.75s 0.5s speaker-test --frequency 2000 --test sine >/dev/null fi sleep $PERIOD done exec 2>&3 exec 3>&-
The beeps will sound through your speakers. Make sure they aren't muted. If you want a beep through a motherboard speaker, look into the