Avoiding Duplicate Purchases: Check Your Inventory First, Then Buy

Published by Adrian Vogel · Reading time: approx. 12 minutes · Last updated: October 2026 · Jurisdiction: Germany

Before you start: This article is not legal advice. What it says about withdrawal and exchange is the basic legal rule for consumers in Germany. Check exceptions, deadlines in your case and the retailer's own terms with the retailer. Or ask a consumer advice centre (Verbraucherzentrale).

In short:

• In the end, you check in seconds before buying whether you already own it.
• You need OWNAMIC on your phone and internet in the shop.
• The look at your inventory before buying takes about ten seconds.
• OWNAMIC does not warn you by itself and keeps no shopping list.

How to record your belongings and find things again is covered in Scan Instead of Search. This article uses that for a different purpose: before you buy something, you check whether you already have it.

What you should know

There are hardly any reliable figures on duplicate purchases as such. How often do people buy something they already own? I found no independent study on that. Closer to it is a 2023 study on wrong purchases in general. It comes from the Nuremberg Institute for Market Decisions (NIM). According to it, around nine in ten people in Germany make wrong purchases from time to time. These are purchases you regret later. Scaled up to the whole country, they added up to almost €9 billion in the twelve months before the survey. Most wrong purchases happen when shopping online. Not every wrong purchase is a duplicate. But the second HDMI cable that ends up unopened in a drawer is one of them.

With food, a duplicate purchase often turns into waste. According to the Thünen Institute, Germany produced almost 12 million tonnes of food waste in 2015. More than half of it came from private households. Not all of that was bought in excess. But two bodies point to the same step before shopping. One is the German consumer advice centres. The other is the "Zu gut für die Tonne!" (Too good for the bin) initiative of the federal agriculture ministry. First you look in the fridge, freezer and pantry. Then you write the shopping list.

Planning helps against impulse buys. According to the consumer advice centres, people who shop without a plan usually buy more than they need. The well-known rules are:

• go with a shopping list
• don't shop hungry
• pause briefly before a spontaneous purchase

The same idea applies to things that are not food. Only there, the stock is not in the fridge. It is in boxes, drawers and the cellar. That is where a look at the inventory helps.

If it happens anyway, it matters where you bought it. Online, consumers in Germany usually have a 14-day right of withdrawal (Widerrufsrecht). This means you can cancel the purchase without giving a reason (sections 312g and 355 of the German Civil Code, BGB). For goods, the period usually starts once you have received them (section 356 BGB). There are exceptions, for example for sealed cosmetics, perishable food or made-to-measure products. In a shop the rule is "bought is bought". An exchange there is a goodwill gesture, a voluntary favour by the retailer. So ask before you buy whether the retailer takes things back.

What OWNAMIC has for this and what it does not

So you know what you can rely on, here is the honest list first.

What does not exist:

• no automatic duplicate detection and no "you already have this" notice when you capture
• no shopping list and no wish list
• no button to mark supplies as used up, and no restock list

The planned purchases in the big picture are something else. They add a future purchase to your wealth planning as a money flow. They do not work as a reminder for the shop.

What does exist:

• the search in the bar and in the inventory list, free and in seconds
• tags on every object, which the search also looks through
• the Amount field on the object and the type Consumable for things you use up
• photos of till receipts, from which OWNY reads the single items with price, quantity and date
• the AI assistant OWNY, which you can ask whether you already have something
• OWNAMIC on your phone's home screen, so you can look things up quickly in the shop

So the way around it is: record the things you often buy twice so they are easy to find. And look them up before you buy.

Step 1: Put OWNAMIC on your phone

In the shop you have no time for detours. So put OWNAMIC on your home screen as an app. This is a web app: it runs in the browser but has its own icon, like a normal app. You do not need to get it from an app store.

• iPhone and iPad:

  1. Open OWNAMIC in Safari.
  2. Tap the share icon.
  3. Choose "Add to Home Screen".
  4. Confirm with "Add".

  Only Safari can put a web app on the home screen of an iPhone or iPad.

• Android: once you have used OWNAMIC in Chrome for a while, the browser offers to install it.

The search needs an internet connection. Without reception, the app cannot help either.

Step 2: Record the typical duplicates first

You do not have to record everything at once. Start with the things people often buy twice. How to film and take photo series is covered in detail in Scan Instead of Search.

Cables, chargers, power supplies. Tip the cable box out onto the table. Lay everything out side by side and record it as a Photo series. Turn the plugs towards the camera. Make sure the print is readable. Create the box itself as a collection, such as "Cable box hallway". Then every result shows its place.

Tools. The "Tools" template creates four collections: Hand Tools, Power Tools, Garden Tools and Materials. You find it under Plus → Template. For cordless tools, a photo of the type plate is worth it. That is the small label with brand, model and technical data. Then brand and voltage end up in the entry. If you own two battery systems, it is easy to buy the wrong charger otherwise.

Supplies. This means screws, wall plugs, batteries, light bulbs, printer cartridges and bin bags. One photo per shelf or box is enough. You enter the amount where it matters. More on that in a moment.

Children's clothes. Children grow faster than anyone can remember sizes. The "Clothes" template gives you a structure. Record clothes by size, one photo series per pile. Give all finds the size as a tag, such as "size 110". Especially with siblings, this shows what is already waiting in the cellar for the next child.

Books. Photograph the bookcase shelf by shelf, spines towards the camera. One shelf per picture is more precise than the whole bookcase from a distance. Then in the bookshop you can check by the title whether the book is already on your shelf.

Food and household supplies. Here the till receipt is the fastest way. Photograph it after shopping like any other photo, flat and straight from above. OWNY reads the single items as consumables with price, quantity and purchase date. Check the finds before you save.

Step 3: Choose names and tags the way you search

The search compares text. It looks at the name first, then the tags, then the description. Part of a word is enough: "HDMI" also finds "HDMI cable 2 m". But it does not know synonyms, meaning other words for the same thing. So whatever you would type in the shop has to be somewhere on the object.

• General word plus feature: "USB-C charger 65 W" instead of "charger". "Cordless screwdriver 18 V" instead of "Bosch".
• The feature the purchase depends on, as a tag: size, connector, power, battery system, format. Examples: "size 110", "USB-C", "E27", "AA".
• For everything at once while capturing: open Additional info, purchase date & tags. In Tags to add to all items, enter what applies to all finds of a capture. For example "cable" or "size 110".
• Afterwards: on the object page, add what is missing under Tags.

Step 4: The ten-second look before you buy

This is the actual habit. Before something goes into the basket, you look it up.

1. On a phone, tap Search at the bottom. On a computer, type into the Search objects... field at the top.
2. Enter the word you are looking for, for example "HDMI" or "size 110".
3. The results show name, description, value and purchase price. The search also includes objects others share with you. For example from a shared household.
4. Tap a result. Under Belongs to you see where the thing is.

Do you want to see the whole way to the thing straight away? Then use the search of the Inventory list. You find it on your start page under More → Inventory list. In the Search inventory… field, every result shows where it lies. For example "My Home › Hallway › Cable box".

The same applies online. Before you tap "Buy" in a shop, open OWNAMIC in a second tab and search. According to the NIM study, most wrong purchases happen online.

Step 5: Ask OWNY when you do not know what it is called

Sometimes you do not know under which name something was recorded. Then ask the AI assistant OWNY. On a phone, tap the OWNY icon in the bottom bar. Ask something like "Do I already have a USB-C to HDMI adapter?" OWNY then searches your objects, including shared ones.

Two things to know. First, every answer uses AI credit, but the search in the bar does not. Second, an AI answer can be wrong. Open the object it names before you rely on it.

Step 6: Keep an eye on supplies

For supplies, OWNAMIC offers building blocks, but no complete stock management. Here is how to use what is there:

• Keep the amount up to date: open the object. Choose Edit all fields in the menu. Enter under Amount what is still there. A receipt photo sets the amount bought. OWNAMIC does not deduct what you use. You update that yourself.
• Add things quickly: for small purchases without a photo, Plus offers Quick entry. It has the fields Name, Type, Purchase Date, Tags and Belongs to. Add saves the entry.
• See recent purchases: do you use the My Household area? Then it shows the consumables of the last 14 days under Consumption · not in contents value. They carry the label Stock. Consumables deliberately do not count towards the contents value there.

For the weekly shop, the consumer advice centres' tip remains the quickest: a short look in the fridge and pantry, then write the list. OWNAMIC adds to that for everything that is not in the fridge.

If it has happened anyway

• Bought online: check whether the 14-day period is still running. You tell the retailer that you are withdrawing. Many shops have a form or a function in your customer account for this. The retailer's terms say whether you pay for the return.
• Bought in a shop: ask for an exchange or a voucher. You have no right to it. But many retailers exchange anyway, as long as the goods are unused and you have the receipt.
• Keep it or pass it on: whatever you cannot return, you can give away, sell or donate. It still belongs in your inventory. Otherwise you may end up with a third one.

Tip: photograph the till receipt or save the order confirmation on the object straight away, with Upload File. Then you have the purchase date and the retailer at hand when you want to check the deadline.

What OWNAMIC does not do here

• OWNAMIC does not warn you about duplicate purchases. It does not spot duplicates by itself, neither when buying nor when capturing.
• OWNAMIC keeps no shopping list or wish list.
• OWNAMIC does not track consumption. The amount stays what you entered until you change it.
• The search does not know synonyms. It only finds what is in the name, tags or description.
• OWNAMIC does not check withdrawal deadlines. It also does not advise you on your rights towards a retailer.
• No connection, no search. OWNAMIC needs a connection for current data.

Video guides

In Help, a short video guide shows how photos and videos become entries. Is your inventory organised by rooms and boxes? Then another one shows how finds get their place.

Checklist to take with you

• OWNAMIC on your phone's home screen
• Cable box, chargers and power supplies recorded as a photo series
• Tools organised with the "Tools" template, battery system in the name
• Supplies recorded shelf by shelf or box by box
• Children's clothes recorded by size, size as a tag
• Bookcase photographed shelf by shelf
• Till receipts photographed after shopping and checked
• Features that decide a purchase added as tags
• Habit set: ten seconds of searching before every purchase, online in a second tab
• Order confirmation saved on the object for online purchases

Read on: Scan Instead of Search · Declutter for winter · Getting organised · Recording your home room by room

Sources

• Nuremberg Institute for Market Decisions (NIM): Fehlkäufe in Deutschland – Das 9-Milliarden-Problem (NIMpulse 2023-3, German): https://www.nim.org/publikationen/detail/fehlkaeufe-in-deutschland-das-9-milliarden-problem
• NIM, press release: Fehlkäufe – das 9-Milliarden-Euro-Problem (German): https://www.nim.org/presse/artikel/fehlkaeufe-das-9-milliarden-euro-problem
• Thünen Institute, press release of 22 September 2021 on food waste, base year 2015 (German): https://www.thuenen.de/media/ti/Newsroom/Presse/Pressemitteilungen/2021/2021-09-22/2021-09-22_LM-Verschwendung.pdf
• Verbraucherzentrale: Buying food cheaply through good planning (German): https://www.verbraucherzentrale.de/node/90044
• Zu gut für die Tonne! (BMEL): shopping notepad, looking in the fridge and pantry first (German): https://zugutfuerdietonne.de/fileadmin/zgfdt/inhalt/Service/Materialdatein/24_BMEL_ZgfdT-2024_Notizblock_105x148_WEB.pdf
• Verbraucherzentrale Hamburg: Exchange and returns – what are my rights? (German): https://www.vzhh.de/themen/einkauf-reise-freizeit/umtausch/umtausch-rueckgabe-welche-rechte-habe-ich
• Section 312g BGB, right of withdrawal for distance contracts (German): https://www.gesetze-im-internet.de/bgb/__312g.html
• Section 355 BGB, right of withdrawal in consumer contracts, 14 days (German): https://www.gesetze-im-internet.de/bgb/__355.html
• Section 356 BGB, start of the withdrawal period (German): https://www.gesetze-im-internet.de/bgb/__356.html

The NIM figures are based on a survey and concern wrong purchases in general, not only duplicates. The legal information reflects the basic rule; exceptions can apply in individual cases.