**Battery-powered leak sensors linked to an internet-connected hub are a good fit for this.** Place one at each likely leak location; the hub sends alerts to your phone.

For a concrete, inexpensive option, I’d consider **YoLink’s hub plus four Water Leak Sensor 1 units**. Its US store currently lists the kit at **$69.99**, with extra sensors at **$16.99 each**. Prices and availability vary by country. [YoLink store](https://shop.yosmart.com/collections/water-leak-sensors-accessories)

The features relevant to your situation are:

- **Free app push notifications.** SMS has a limited free monthly allowance; additional messages require a paid plan. [Notification details](https://support.yosmart.com/hc/en-001/articles/17988570459161-YoLink-App-Q-As)
- **Replaceable AAA batteries**, with a manufacturer-rated life of five-plus years. Treat that as an estimate and check batteries periodically. [Sensor datasheet](https://www.yosmart.com/wp-content/uploads/YOLINK-YS7903-WATER-LEAK-SENSOR-1-DATASHEET-090322-2.pdf)
- **Detection of dripping and pooling water.** Sensor 1 has no built-in audible alarm, so keep your existing beeping alarms alongside it. For awkward spaces behind appliances, Sensor 2 offers a sensing cable. [Sensor comparison](https://shop.yosmart.com/pages/water-sensors)

Placement and testing matter as much as the brand:

1. Put sensors where escaping water will collect: beneath sink connections, beside toilet supply valves, and below the refrigerator’s water connection. Water must reach the sensor to trigger it.
2. Test every sensor with water in its intended location, then dry it. Confirm you receive an alert while your phone uses cellular data.
3. Enable notification sounds and any available low-battery/offline alerts. Repeat the water test periodically.

**Remote alerts depend on power, your home internet connection, and the provider’s service.** YoLink explicitly requires an internet connection for app functionality. A small UPS for the hub, router, and modem can cover brief power cuts; an internet outage still interrupts remote alerts. [Hub requirements](https://shop.yosmart.com/pages/system-builder-water-leak-protection)

Given your previous upstairs flood, an **automatic water shutoff** is also worth considering as a later upgrade. A notification gives you time to respond; a properly installed shutoff can stop the supply while you’re away.