Setting up a little notification system to alert you when the laundry is finished is a time-honored DIY electronics project. If you fancy using a Raspberry Pi Zero for one, GitHub user Shmoopty shares his project.
Using a vibration sensor, the Pi monitors vibrations and sends you an alert when the device starts or stops vibrating. The notification can come through either Twitter or PushBullet. This way, if your washer and dryer are tucked away deep inside your house and you miss the alarm, you hopefully won't forget about the clothes you're washing. Head over to GitHub for the full guide to make it for yourself.
Raspberry Pi Appliance Monitor [GitHub]