A slightly modified version of https://github.com/liviu-/ding (OS X only)

ding

#!/usr/bin/env python
"""Simple CLI beep tool"""

from __future__ import unicode_literals
from __future__ import print_function

import os
import sys
import time
import datetime
import subprocess

EXIT_MSG = """Invalid arguments: {}\n---------
$ ding at hh[:mm[:ss]]
$ ding in \d+[smh]( +\d+[smh])*
Examples:
    $ ding at 15:30
    $ ding in 5m 30s
"""

VERSION = '1.2.0'
N_BEEPS = 1
WAIT_BEEPS = 0.05


class InvalidArguments(Exception):
    pass


def check_input(args):
    """Validate user input"""
    if len(args) < 2 or args[0] not in ['in', 'at']:
        raise InvalidArguments('insufficient number of arguments')

    if args[0] == 'in':
        if not all(arg.endswith(('s', 'm', 'h')) for arg in args[1:]):
            raise InvalidArguments('please use s/m/h suffixes')
        if not all(arg[:-1].isdigit() for arg in args[1:]):
            raise InvalidArguments('please use numbers for specifying the duration of time units')

    if args[0] == 'at':
        if len(args) > 2:
            raise InvalidArguments('too many arguments')
        if not all([arg.isdigit() for arg in args[1].split(':')]):
            raise InvalidArguments('there should only be numbers optionally separated by ":"')
        # Valid time
        try:
            datetime.time(*map(int, args[1].split(':')))
        except ValueError as e:
            raise InvalidArguments(e)

    return args

class TimeParser():
    """Class helping with parsing user provided time into seconds"""
    time_map = {
        's': 1,
        'm': 60,
        'h': 60 * 60,
    }

    def __init__(self, time, relative):
        self.time = time
        self.relative = relative

    def get_seconds(self):
        return self._get_seconds_relative() if self.relative else self._get_seconds_absolute()

    def _get_seconds_relative(self):
        return sum([self.time_map[t[-1]] * int(t[:-1]) for t in self.time])

    def _get_seconds_absolute(self):
        now = datetime.datetime.now()
        user_time = (datetime.datetime.combine(datetime.date.today(),
                                               datetime.time(*map(int, self.time[0].split(':')))))
        return ((user_time - now).seconds if user_time > now
                else (user_time + datetime.timedelta(days=1) - now).seconds)


def print_time(seconds):
    """Print countdown for `seconds`"""
    while seconds > 0:
        start = time.time()
        os.system('cls' if os.name == 'nt' else 'clear') # accommodate Windows
        print(datetime.timedelta(seconds=seconds))
        seconds -= 1
        time.sleep(1 - time.time() + start)


def beep(seconds):
    """Make the beep noise"""
    for _ in range(N_BEEPS):
        subprocess.call(["afplay", "/System/Library/Sounds/Glass.aiff", "-v", "15"])
        time.sleep(WAIT_BEEPS)


def parse_time(args):
    """Figure out the number of seconds to wait"""
    relative = True if args[0] == 'in' else False
    user_time = args[1:]
    parser = TimeParser(user_time, relative)
    return parser.get_seconds()


def main(args=sys.argv[1:]):
    if args and args[0] == '--version':
        print(VERSION)
        sys.exit()
    try:
        seconds = parse_time(check_input(args))
    except InvalidArguments as e:
        sys.exit(EXIT_MSG.format(e))
    print_time(seconds)
    beep(seconds)

if __name__ == '__main__':
    main()

LICENSE

MIT License

Copyright (c) 2016 

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.