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For most rainwater systems, SJE Rhombus is one of the strongest companies to consider for a simple, dependable high- or low-water tank alarm. Its Tank Alert line is built around float switches, loud local alarms, warning lights, and weather-resistant enclosures. Some versions can also connect to other controls or remote warning devices.
However, it is not the best choice for every tank. Proteus is a better fit when remote Wi-Fi alerts matter, while TankMate is better suited to continuous tank-level monitoring rather than a basic on/off alarm.
As of September 1, 2026, the best company depends mainly on what you want the alarm to tell you.
Best Water Tank Alarm Companies by Use
| Company | Best fit | How it monitors water | Main consideration |
|---|---|---|---|
| SJE Rhombus | Simple high- or low-level alarms | Float switch | Strong choice when a loud, local alarm is the priority |
| Proteus | Remote alerts and smart monitoring | Float, non-contact, or distance sensor options | Usually depends on Wi-Fi for remote functions |
| TankMate | Continuous rainwater tank monitoring | Non-contact radar | More of a tank-monitoring system than a basic alarm |
There is an important difference between an alarm and a level monitor.
A basic alarm watches one point in the tank. For example, a float may trigger when the tank becomes almost empty or almost full.
A level monitor measures changing water depth. It can show that a tank is 70% full today and 45% full later. Some systems then let you set high- and low-level alerts.
If you only need to know when something has gone wrong, a simple alarm is often the easier system.
Why SJE Rhombus Is a Strong Overall Choice
SJE Rhombus focuses heavily on liquid-level controls and alarms. Its Tank Alert systems can be configured for either a high-water or low-water warning depending on the float switch being used.
That makes the company useful for several rainwater-system problems.
A low-level alarm can warn you before a storage tank becomes empty enough to cause problems for a pump.
A high-level alarm can warn that water has reached an unusual level. This can be useful where a normal overflow path should keep the tank from reaching that point.
Some SJE Rhombus alarm systems are designed for indoor and outdoor installation. For example, the Tank Alert EZ has a Type 3R enclosure, while the Tank Alert 4X uses a NEMA 4X enclosure intended for indoor or outdoor service.
Several models also provide both a horn and a visible warning light. Some include auxiliary contacts that can be connected to another compatible warning or control device.
When SJE Rhombus makes the most sense
Consider this type of system when you want:
- A clear alarm instead of detailed tank-level data
- A high- or low-water warning
- An audible alarm at the tank, pump area, or nearby building
- Equipment designed specifically for liquid-level control
- An outdoor-rated alarm enclosure where required
- The option to connect the alarm to other compatible controls
One useful feature is the ability to place the alarm on a circuit separate from the pump on compatible systems. That way, a pump-circuit failure does not automatically remove power from the warning system.
That setup involves mains electricity, so wiring and circuit changes should follow the manufacturer's instructions and local electrical requirements. Use a qualified electrician where required.
When Proteus Is the Better Company
Proteus makes more sense when you want the water tank to send an alert to you rather than only sounding a horn nearby.
Its L5 system can use a float switch to detect whether water has moved above or below a chosen point. It can provide local audible warnings along with email, text, and other remote notifications.
Proteus also offers different sensing approaches. Its current L5 system supports float-switch, non-contact, and laser-based level sensing options. The laser version can be used for continuous level measurements rather than just detecting one alarm point.
That makes Proteus useful for a homeowner who wants to check a rainwater cistern from another building or receive a warning while away.
The main limitation
Remote monitoring adds more parts that must keep working.
You may depend on:
- Electrical power
- Wi-Fi
- Internet access
- Correct notification settings
- Cloud or communication services
A local float alarm is simpler because it does not need an internet connection to make noise.
For a critical low-water condition that could affect a pump, do not assume a phone notification is the only protection you need. A proper pump system may also need dry-run protection, which shuts a pump down when there is not enough water available.
An alarm tells you about the problem. Dry-run protection can help stop the pump automatically.
When TankMate Is the Better Choice
TankMate is aimed more at measuring how much water remains in a tank.
Its current R3 sensor uses non-contact radar installed above the water. The company offers Wi-Fi and cellular versions, and its app can display tank level and related water-use information.
This approach can be helpful for rainwater storage because the sensor does not need a float hanging at one fixed alarm point.
TankMate's system can also provide low- and high-level push notifications through applicable app features.
It may be a better fit if your main question is:
"How much water do I have left?"
A basic SJE Rhombus-style alarm is a better match when your question is simply:
"Has the water crossed this dangerous level?"
Check the installation requirements first
Non-contact monitoring does not mean no installation work is required.
TankMate's current R3 installation requires an opening in the top of the tank and clear positioning above the water surface. Tank shape and installation geometry therefore matter.
Do not drill or cut a tank until you have checked the manufacturer's installation requirements and made sure the work will not damage the tank.
Float Alarm or Non-Contact Sensor?
This choice often matters more than the company name.
Float switches
A float switch moves as the water rises or falls. At a chosen point, the switch changes state and activates the alarm.
Float switches are simple and widely used.
They work well when you only need to detect one condition, such as:
- Almost empty
- Almost full
- Water above a pump intake
- Water reaching an abnormal level
The sensor must normally be installed inside the tank, so access and sensor material compatibility matter.
Non-contact sensors
Look closely at causes of high-water alarm activation to compare how the decision supports the whole collection process.
A non-contact system measures the water without placing the main sensing element underwater.
Depending on the system, it may use radar, optical distance measurement, or another sensing method.
These systems are useful when you want continuous readings or want to avoid a submerged moving float.
However, they can be more sensitive to installation position, tank shape, internal pipes, narrow openings, condensation, or other conditions depending on the sensing technology.
Always follow the manufacturer's limits rather than assuming any non-contact sensor will work on any tank.
What to Check Before Choosing a Company
Start with your water system rather than the alarm brand.
Decide what condition matters
Choose whether you need:
- High-level warning
- Low-level warning
- Both high and low warnings
- Continuous tank level
- Remote phone alerts
- A local horn and light
- Automatic pump shutdown
These are different jobs.
A monitor that sends a phone notification is not automatically a pump controller. Likewise, a simple high-water float alarm will not tell you that the tank is 42% full.
Check the tank
Confirm:
- Tank material
- Tank height
- Access opening
- Maximum water level
- Safe sensor mounting point
- Distance from the tank to the alarm panel
- Whether installation requires drilling
An IBC tote may need a different setup from a large polyethylene rainwater tank or an underground cistern.
Check the power source
Some alarms plug into mains power. Others use batteries.
Remote systems may also need Wi-Fi or cellular coverage.
For outdoor installations, confirm that every part exposed to weather is actually rated for that location. Do not assume an indoor plug-in alarm can simply be mounted outside under a small cover.
Think about what happens after the alarm sounds
An alarm is useful only if someone can act on it.
For a low rainwater tank, the response may be switching the pump off or changing to another approved water source.
For an unusually high tank level, the response may involve checking the overflow, screens, pipes, or drainage route.
The alarm should not be used as a substitute for a correctly sized and maintained overflow.
Water Tank Alarms Do Not Measure Water Quality
A level alarm tells you where the water is.
It does not tell you whether the water is safe.
The alarm cannot determine whether roof runoff contains bacteria, metals, chemicals, animal waste, or other contaminants.
This matters especially if collected rainwater could be used for drinking or other household purposes.
For drinking-water use, treat the entire system as one water-quality system. Collection surfaces, debris removal, first-flush management, storage, treatment, maintenance, current laboratory testing, and applicable local requirements can all matter.
Also check whether any sensor that touches stored water is suitable for the intended water use. Do not assume that a float or cable intended for non-potable water belongs inside a tank supplying drinking water.
Potable means suitable for drinking. Non-potable water is water that is not intended for drinking.
A non-contact sensor can reduce contact with the stored water, but it still does not make untreated rainwater potable.
Which Company Should You Choose?
For a typical rainwater system where the goal is a dependable high- or low-level warning, SJE Rhombus is a strong overall company to start with. Its alarm systems are purpose-built for liquid-level warning, and the company offers options for different environments and float configurations.
Choose Proteus instead when remote Wi-Fi alerts and flexible sensor options are more important.
Choose TankMate when you want to follow the actual amount of water in a rainwater tank over time rather than simply trigger an alarm at one level.
The best system is the one that matches the condition you need to detect, fits your tank, works with your available power and communications, and still gives you a useful warning when something goes wrong.
Frequently Asked Questions
What is the best company for a simple water tank alarm?
SJE Rhombus is a strong option for a simple high- or low-level alarm. Its Tank Alert systems are designed specifically for liquid-level warning and include float-switch configurations, horns, warning lights, and indoor or outdoor options.
Can a water tank alarm tell me how full my tank is?
Not always. A basic float alarm normally detects whether water has crossed one set point. Continuous monitors such as radar or distance-based systems can provide changing water-level readings.
Should I install a high-level or low-level alarm?
For many rainwater tanks, a low-level alarm is useful for warning that stored water is running out. A high-level alarm may be useful where reaching an unusual level could indicate an overflow or drainage problem. Some systems can monitor both conditions.
Can a low-water alarm protect my pump?
It can warn you, but an alarm does not necessarily shut the pump off. If running dry could damage the pump, look at proper dry-run protection or a compatible pump controller in addition to the alarm.
Are Wi-Fi water tank alarms reliable without internet?
Their local alarm functions may vary, but remote phone or email notifications generally depend on communication services. Check the specific system. If the warning is critical, consider whether you also need an independent local alarm or automatic control.
Can I put a float switch inside a drinking-water tank?
Do not assume every float switch is suitable for potable-water contact. Check the manufacturer's stated application and materials for every wetted component. Drinking-water rainwater systems also require appropriate collection, treatment, testing, maintenance, and compliance with applicable local requirements.
Is a non-contact water level sensor better than a float switch?
Neither is always better. A float switch is simple and well suited to a single alarm point. A non-contact sensor is useful when you want continuous measurements or do not want a submerged moving sensor. Tank shape, installation space, power, communications, and maintenance should guide the choice.
