What’s a reliable way to monitor server-room temperature, humidity, and AC leaks?

If you already have Room Alert hardware, staying with that ecosystem is probably the simplest option. Ask the vendor whether your current unit can support an additional leak sensor through an expansion device; otherwise, the larger model should give you more inputs. A leak detection cable is often better than a small point sensor because it can cover the entire area beneath and around the AC unit.

For an on-premises option, an RLE-style facility monitor with leak cable, temperature, humidity, and door inputs can feed data into an existing monitoring platform such as Zabbix. It’s more involved than a cloud appliance, but it gives you historical data and control over alerting. The important part for this situation is choosing a proper sensing cable rather than just placing a single water probe under the condensate pump.

Whatever system you choose, avoid relying on only one alert path. Use email plus text or phone alerts, and make sure you can detect when the monitoring device or network connection goes offline. A separate leak detector or independent sensor can provide useful redundancy, since the main environmental monitor may be affected by the same power or network problem it is supposed to report.

APC NetBotz or a rack-monitoring system can handle temperature, humidity, doors, and leak sensors, especially if you already use APC UPS equipment. It works well, but I wouldn’t buy into that ecosystem solely for one water sensor unless you already have compatible hardware. Some UPS network cards also accept environmental sensors, but those sensors are usually proprietary and expensive.

There are several cloud-based options that handle temperature, humidity, and water sensors with threshold-based email alerts. Ubibot and SensorPush are relatively straightforward, while Monnit and Sensaphone offer a broader range of sensors and more mature alerting features, including text messages and call trees. Check the ongoing subscription costs and whether the sensor requires a local gateway or cellular connection.