An extra minute in a hotel shower can feel remarkably good value. You have already paid for the room, the water is warm, and staying a little longer will not add anything to the bill. At least, not the one you receive at checkout. For the hotel, that minute still costs money. Repeat it across hundreds of guests and the gap between who enjoys the water and who pays for it becomes an interesting business opportunity.

Danish company Aguardio has built a device around that gap. Its shower sensor monitors how long the water is running and displays the time to the person using it. The guest remains in control of the tap. The idea is that seeing the minutes pass might encourage them to finish a little sooner. It is a modest intervention, although putting a timer in someone’s holiday bathroom does require a certain confidence in human nature.

The economic problem is straightforward. A hotel has a reason to reduce its utility costs, while a guest has little immediate financial incentive to help. That does not mean guests are indifferent to wasting water. Someone can care about the environment and lose track of time under a warm shower. Aguardio’s proposition depends on bringing that decision to their attention while they can still do something about it.

There is evidence that this can work. A study published online in 2024 in the Journal of Travel Research tested Aguardio’s technology. In one experiment, researchers analysed 1,301 showers across 20 rooms at a four-star, all-inclusive Spanish beach resort during the winter of 2019–2020. Water ran for roughly 26% less time in rooms with a visible timer than in rooms where the sensor collected data without displaying it. The research involved collaboration with Aguardio, but measured actual behaviour against a control group. It gives the company something more useful than a survey of good intentions.

Still, 26% less time with the water running is not a 26% reduction in the hotel’s water bill. The experiment measured duration, rather than directly metering the litres saved. Turning that result into euros requires knowing the shower’s flow rate, the cost of water and the energy needed to heat it. Kitchens, laundries and swimming pools also remain on the bill. A promising result in one resort gives another hotel a reason to test the product, rather than a saving it can simply copy into its budget.

Aguardio’s published indicative price is about €130 per shower sensor, including three years of data subscription, with discounts for larger orders. Spread over those three years, the purchase alone would require savings of approximately €3.61 per room each month to recover its cost. That is a simple calculation, not a forecast of what a hotel will save. Installation, upkeep and any additional service or connectivity costs belong in the calculation too.

Occupancy matters just as much. A device in a busy room has more opportunities to save water than one sitting in an empty room through the winter. Expensive hot water could strengthen the case; an efficient shower that guests already use briefly could weaken it. For a founder selling this kind of product, a percentage on a presentation may get a meeting. A convincing estimate based on the buyer’s own property is more likely to get an order.

Then there is the work of keeping everything running. Aguardio’s maintenance guidance says that limescale on the sensor’s front frame can interfere with shower detection, and the device has a replaceable battery. Neither makes it impractical, but both belong in the operating plan. Someone has to clean the units, check faults and deal with replacements. A small task repeated across a hotel can become a meaningful expense, particularly if it creates another thing for housekeeping to remember during an already busy shift.

The guest presents a different calculation. A hotel is asking someone who has paid to relax to pay attention to their consumption. Some may appreciate the reminder. Others may wonder why a business charging them for a comfortable stay is suddenly so interested in their third minute of hot water. Shorter showers alone cannot tell us which reaction the device produced. A guest can comply with a request and still find it irritating.

A 2019 qualitative study by Denmark’s Alexandra Institute offers some insight. Through observations and interviews at Hotel Sixtus in Middelfart and Danhostel in Kalundborg, researchers found that guests generally responded positively when the device was explained as part of the property’s environmental approach. An unexplained box caused uncertainty: guests wondered whether it was a humidity sensor, an air freshener or a surveillance camera. The institute also helped develop Aguardio’s software and platform, so this was feedback from a development partner, rather than an independent customer-satisfaction audit.

Aguardio states that the shower sensor has no camera. Even so, a hotel should explain what the device measures and how the information is used. Discovering unfamiliar technology while standing naked is hardly the ideal introduction to a company’s data practices. Clear communication could make the difference between a useful prompt and something a guest covers with a flannel. It also gives reception staff an answer when someone inevitably asks what the little box is doing.

The hotel’s wider behaviour matters here. A request to save water is easier to take seriously if a reported leak gets fixed promptly. Equally, there is no need to pretend that reducing costs somehow discredits the environmental benefit. Using less hot water can help both. The difficulty comes when the guest feels that every saving requires them to give something up, while the hotel’s own responsibilities remain out of sight.

Aguardio also sells toilet leak sensors and now markets monitoring for water, heating and cooling systems more broadly. That gives it a route beyond persuading guests. Detecting a leaking toilet addresses waste the hotel can tackle directly, without asking anyone to shorten a shower. However, an alert still needs to reach someone who can arrange a repair. The commercial value depends on what happens after the system identifies a problem.

For the startup, these are connected but distinct sales arguments. Shower feedback relies on a guest changing their behaviour; leak detection relies on the hotel changing its maintenance response. Selling both could make the customer relationship more valuable, but it also creates more work around installation, support and reliable data. Expanding the product range helps only if the additional revenue covers that work and the customer can see why the service is worth keeping.

A useful hotel trial would therefore examine utility savings alongside staff time and guest feedback. Comparing similar rooms over the same period would help separate the device’s effect from changes in occupancy or season. Managers would also need to check whether the savings persist after the initial attention wears off. Those results would give a hotel group a stronger basis for expanding an order, and give Aguardio a more persuasive case for its next customer.

There is a credible business possibility in making an everyday cost easier to see. Aguardio has evidence that feedback can change behaviour, and a buyer with a reason to care about the result. Its harder task is making the savings reliable enough, and the experience comfortable enough, for hotels to keep paying. The guest may never see the water bill. The hotel deciding whether to buy another hundred sensors certainly will.