DIY battery replacement

At a glance

Title: Replacing technician visits with app-based DIY battery replacement for Sector Alarm

One-liner: Reminding and guiding customers through in-app DIY battery replacement results in approximately €70 000 of monthly savings by increasing replacement rate from 50% to 60%.

Role: Sole designer, responsible for discovery, UI, UX and research. Commercial model owned by PM.

Team: Designer (me), PM, engineering pod of 6 – front/back-end + QA

Timeframe: Jan–Jun 2026

Context: Sector Alarm is the second biggest B2C alarm system company in Europe, their alarm system comes with iOS and Android native mobile apps. The digital solution battery replacement solution was built to complement existing SMS and phone-based battery replacement reminder and shipping service.

Hook

When a customer doesn't replace a low battery themselves, Sector Alarm has to send a technician to their home to do it. The customer has to pay for the visit (which drives dissatisfaction), but even with a partial cover Sector Alarm still loses money on the visit. Around half of customers don't replace batteries themselves in time, which initiates the costly manual process.

Problem

Alarm system consists of several components such as window and door sensors, motion detectors, and smoke detectors. Each of them is powered by a disposable battery which has to be replaced every few years. Previously, when a battery was low, the company would send replacement batteries by mail. To inform them they would send an initial SMS, followed by a reminder SMS on day 3, 7 and 14. The package contained the batteries and a piece of paper with links to the company's website where the user could find instructions on how to replace the batteries.

The problem with this approach was that only about half of the users would end up replacing the batteries themselves. The biggest obstacle to replacing the batteries, cited by the process owner (the person responsible for the existing SMS reminders and mailed batteries) and users themselves (feedback collected via a survey from 100 users who replaced batteries themselves), was perceived complexity. The survey pointed to where that perception bites: locating the sensor in their home, taking it off the wall and opening it up to access the batteries was the step users found scariest to initiate. But when asked about the impression of the process overall, most found it quite easy. Furthermore, most users said that the thing that finally convinced them to replace the batteries were SMS reminders.

When a user is unwilling to replace the batteries, the company has to send a technician to the user's home. This is costly for both the company and the user, as they also have to pay for the visit, but, since the payment doesn't fully cover the visit, the company is also losing money on every dispatch.

[Image — customer journey map]

Opportunity

How might we use the app to better remind users that they need to replace the batteries, guide them in the process and provide feedback if they did it correctly.

Why it matters

Every time a user replaces batteries themselves it means no technician needs to be sent to customer's home, which saves Sector Alarm around €50 per visit. If we do a good job at automatically guiding the user through the process and give clear feedback, the user won't need to contact customer support, which also saves money. If we can increase overall battery replacement rate at least 10% that would result in hundreds of thousands of euros in savings each year.

Success criteria

The overall company objective was to simplify field operations. Our key result for version 1 was to lift the DIY battery replacement rate from around 50% to 60% in the quarter after launching the feature.

What made it hard

Our goal was to increase the battery replacement rate as much as possible and, thanks to the customer survey, we knew that the main hurdle for users was simply starting the task and the main motivator that nudged them were the SMS reminders. Therefore, we made the hypothesis that by nudging users more often and reminding about the stakes (alarm system functionality might be affected if batteries are not replaced in time) was out best bet to affect the replacement rate.

On the other hand, Sector Alarm is positioned as a premium product, and customer satisfaction (CSAT) is one of the main metrics we track – so sending too many notifications of increasing urgency might cause frustration, decreasing CSAT and app retention in the process.

The hard part was finding the right balance of urgency (the copy and design of the notifications themselves) and the frequency of the notifications.

Approach

Discovery

I interviewed stakeholders who are responsible for the current battery process and country managers to get their sense of the service experience. Then I conducted a survey of existing customers (100 respondents) who had replaced their batteries to understand their experiences. I also benchmarked similar services in our competitor products and wider smart home market.

Drafting a vision

Because this was a complicated service, with several legacy dependencies and risks, I knew that we couldn't completely rebuild the service in the first pass. So I decided to create a wider vision for the service – how could the best case scenario look like, if there were no immediate constraints. This helped guide the team in scoping and keeping a further horizon in mind while building version 1.

[Image — vision board]

Constraints

Since a process was already in place – batteries sent by mail, customers informed by SMS – we chose first to complement that existing flow with in-app reminders and guidance running in parallel. This constrained our communication strategy. And because of limited time, we chose not to build step-by-step instructions in version 1; we included only instructional videos.

Design decisions

Comms strategy

The best ways to communicate about the batteries were in-app and push notifications. In the app itself we had three types of message: blue, yellow and red. Blue was the lowest priority, yellow and red the higher ones.

[Image — the three message types (blue / yellow / red)]

We wanted to communicate that the batteries need to be replaced in time or the sensors might stop working. For low urgency tone we could use dismissible blue messages, for medium – yellow, and for highest urgency – red.

We decided to use blue messages on day 1, when we inform the user that the batteries need replacing and that replacements have been sent, and then red, non-dismissible ones on days 7 and 14. We considered using the yellow messages on day 7 and then escalating to red on day 14, but we decided to escalate to red straight away in order to communicate that replacing the batteries is an urgent and important task. The red messages would stay visible until user replaced the batteries.

We decided to use blue messages on day 1, when we inform the user that the batteries need replacing and that replacements have been sent, and then red, non-dismissible ones on days 7 and 14. This might annoy some users, but we decided to lean on a stronger tone of voice in v1 in order to keep the task at the top of users' minds. We would watch for negative movement in CSAT score and user feedback (via app reviews and customer support) after version 1 launched and tune the messaging down if needed.

[Image — user journey map with explanation]

Guidance design

In discovery we identified that one of the biggest blockers for replacing the batteries was difficulty in locating the sensor and fear of breaking it. To address this I included a "Battery replacement guide" that opens when the user clicks the reminder notification on the home screen. In the guide, the user can see exactly where the sensor is located in their home and see an animated video on how to take the sensor off the wall, open it and replace the battery. I also addressed the fear of not doing it correctly with visual feedback once the sensor is back on its wall bracket and online – the user can see it working again.

What shipped

[Image 1]

Day 1: first notification – blue, dismissible. Tells the user that batteries need replacing and that replacements are on the way by mail.

[Image 2]

Day 7: escalates straight to red and can't be dismissed – it stays on the home screen until the batteries are replaced or the day 14 reminder replaces it.

[Image 3]

The battery replacement guide – which sensors need new batteries and where they are, confirmation that replacements have been sent, and video instructions. Once the sensor is back on its bracket and online, the app confirms the replacement worked.

[Image 4]

Low battery reminders also appear on other pages where sensor information is shown.

Outcomes

In the first three months after shipping version 1, battery replacement rate increased from around 50% to 60%. At the time Sector Alarm had around 15,000 low-battery events per month, so a ten-percentage-point lift meant roughly 1,500 additional DIY replacements each month. Each avoided technician visit saved the company €30–50 net, so the lift was worth roughly €45k–75k a month, or €540k–900k a year.

User experience also improved. Instead of dealing with customer support, paper instructions and support pages on the website, users could now find everything they needed by opening the app. According to Customer Support, the volume of customer support requests related to battery replacement decreased by around 30% in the same period (this is a rough estimation).

Reflection

A big challenge while working on this feature was not being able to get feedback about the effectiveness from real users. This feature is closely tied to the long-term experience of owning an alarm system, so testing it online with panel users would have been superficial. To properly test, we would have needed to be with a customer during the time when they change the batteries or interview them after the fact. Because of concerns about annoying users who already had low engagement with the product, we decided not to pursue feedback from users who hadn't replaced batteries themselves – we only engaged the ones who had. We had to assume that users who did replace the batteries themselves had similar mental models to ones who didn't. If I started from scratch, I would push to engage the passive users more, despite the risk of them getting annoyed.

Although we saw an increase in the number of users replacing batteries themselves after launch, we saw no clear signal about the cost of the more aggressive red-message approach. It may be one of those things that slightly degraded the overall experience without registering in the feedback.