A simple linux cli timer that alerts with sound and notification. ./timer.sh -m <minutes or -s <seconds> or by default if nothing is passed it will do 30 minutes.

timer.sh

#!/bin/bash

# ./timer.sh -h 1
# ./timer.sh -m 30
# ./timer.sh -s 10  for 10 seconds
# ./timer.sh -e 1h10m30s
# ./timer.sh -m <message>
seconds=1800;
message="Times Up!!!!"
#checks for -s or -m else defaults to 30 minutes
if [ -n "$1" ]; then 

	if [ $1 == '-s' ]; then 
		seconds=$2
	fi

	if [ $1 == '-m' ]; then 
       		seconds=$2*60
	fi
	
	if [ $1 == '-h' ]; then 
       		seconds=$2*3600
	fi       
	
	if [ $1 == '-e' ]; then
		[[ $2 =~ ([0-9]+h) ]] && hours="${BASH_REMATCH[1]}"
		[[ $2 =~ ([0-9]+m) ]] && minutes="${BASH_REMATCH[1]}"
		[[ $2 =~ ([0-9]+s) ]] && secondsnew="${BASH_REMATCH[1]}"
		hours="${hours//h/$''}"
		if [ -z "$hours" ]; then
			hours=0
		fi
		minutes="${minutes//m/$''}"
		if [ -z "$minutes" ]; then
			minutes=0
		fi
		seconds="${secondsnew//s/$''}"
		if [ -z "$seconds" ]; then
			seconds=0
		fi
		hours=$((3600*$hours))
		minutes=$((60*$minutes))
		seconds=$(($seconds+$minutes+$hours))
	fi
fi

if [ -n "$3" ]; then 
	if [ $3 == '-m' ]; then 
		message="$4"
	fi
fi




date1=$((`date +%s` + $seconds));\
while [ "$date1" -ge `date +%s` ]; do    echo -ne "$(date -u --date @$(($date1 - `date +%s` )) +%H:%M:%S)\r";  done; notify-send -u critical $message && paplay /usr/share/sounds/ubuntu/ringtones/Alarm\ clock.ogg

Adding a "sleep 1" after echoing counter will reduce CPU usage.