Samsung SmartThings Arrival Sensor Price: $29.99 $24.99 (as of 18/04/2019 00:06 PST- Details) & FREE Shipping.

Get alerts when people and pets approach and leave a specified area, such as a home or office.
Trigger different actions to take place when you arrive or leave home, such as automatically turn the lights on or off, or lock or unlock the door.
Be notified if someone doesn’t arrive home by a certain time.

Usually ships in 24 hours