This Set Of Three Wifi Door Sensor Detectors Is Compatible With Alexa And Google Product Details Receive Real-time Alarms Remotely:when door/window is opened or closed, the sensor will push instant notification to your smartphone immediately. so you don't have to worry about your baby going out of house without notice, will easily know when your aged parents leave or arrive home and even can be clear when someone enters your home,shop,office ,etc. Compatible with Google Play,Andriod and Ios System:No hub required and No fees charge. Convenient for you to detect the status of your doors, windows, cabinets, drawers or anywhere you want to notified when it is opened or closed.So you can travel or go to work or go to schoon or go shopping worry-free. Alert message push: Protect your home with open / closed door detection. When the door / window is triggered, you will receive an alarm signal from your phone. Home Security Alarm make House more safety. Easy Installation?No Need to use complicated tools when installation,just use 3M glue to install,firm and durable.The two arrows are opposite,the distance between the two compopents should be as close as possible,and the closest distance should not affect the opening/clsoing of the door or window. Low Power warning: The sensor door need with TWO AA Batteries(not include).When the battery level is low, it will automatically push messages throuch APP to remind you to change battery, never worry about running out of battery. Payment We accept PayPal and credit cards via PayPal. Taxes - US We collect sales tax, as required by law. Shipping We make every effort of shipping within 3 business day of payment clearing. The estimated delivery time is 2 - 5 business days from the shipping date. Policies If you do need to return your item, please contact us via email (you will receive an email when your product ships with additional details - Subject: Important information about your purchase). You will then be provided with a return shipping label and packing slip. Pack the item carefully. Include the packing slip, apply the shipping label, and return the item within 30 business days of the date you request a return, or your return will be canceled. Once we receive your order we will inspect the return. Please allow up to 5 business days of receiving the returned item for your refund.