Do you ever feel like the supermarket self-checkout machine just freezes up when you tap the wrong thing?
Last weekend I went on a tour around town to find out how fast the self-checkout machines from different UK retailers really are.
Methodology
After setting off, I quickly learned that there's no self-checkout in Booths. The first Aldi I went to was closed due to a freezer gas leak. Ultimately, I managed to try the self-checkout at 8 different stores:
- TGJones (née WH Smith)
- Boots
- Tesco
- Sainsbury's
- Marks & Spencer (M&S)
- Lidl
- Aldi
- Asda
At each one I went through self-checkout while recording a slow-motion video on my phone. Where possible I tried to buy an item without a bar code, such as an orange or pastry. When that was not an option I opened the "enter barcode" flow and entered a number there before cancelling.
To collect the metrics, I went through each video and recorded the time of the interaction and the time when the next screen was fully rendered. For the analysis I then identified the slowest interactions for the product selection process and the checkout process.
Findings
Overall, most individual interactions were fast, taking around 200 to 400 milliseconds before the next screen is shown. However, several machines also had delays of over one second between the tap on the screen and when the new UI was rendered.
Aldi and Lidl were fastest, with all interactions taking less than 400 milliseconds.
What were the slow interactions?
- The Boots machine froze for over 3 seconds after tapping "I don't have an Advantage Card"
- TGJones froze for 1.5 seconds after declining their Premier League promotion offer
- Asda froze for over 1 second after selecting the product quantity and after selecting "No bags"
- The Sainsbury's machine took 0.7 second to render the item after confirming the quantity
What were the fastest interactions?
Entering a number for during quantity selection (without adding the item to the basket) usually takes less than 200 milliseconds.
😋 Adding an apple turnover to the basket at Lidl takes just 150 milliseconds! Here's a slow motion video so you can truly enjoy the experience.
Unnecessary steps slow down the checkout process
Right before payment, some checkout terminals ask additional questions:
- Do you have a membership card?
- Do you want to purchase promotion items?
- Do you want any bags?
- Do you want to round up for a charity donation?
In contrast, other shops remind you to scan your membership card purely based using visual and auditory alerts, without an explicit confirmation.
| Shop | Extra Steps |
|---|---|
| Lidl | Bag Selection, Membership |
| TGJones | Promotion, Bag Selection |
| Tesco | Charity Donation |
| Sainsbury's | Bag Count |
| Asda | Bag Selection |
| M&S | Bag Selection |
| Boots | Membership |
| Aldi | None |
Sainsbury's doesn't let you pay by card until after you've selected a payment method. In contrast, most other stores just let you tap your card once you're ready to pay.
Quantity selection
During quantity selection some shops default to a quantity of one. Others make you enter a number before confirming it, requiring an extra button tap.
Other observations
Instant interaction feedback
Not every tap interaction is registered correctly. Some checkout machines provide a quick confirmation of each input, long before the next screen has rendered.
Here we can see Sainsbury's showing a gray circle after selecting single red onions.
Fade transitions are common
Transitions between screens are not always instant. Often one screen fades out while the other one fades in.
In this example from Aldi we can also see that after selecting an item, the machine first briefly fades in the root checkout screen before fading in the quantity selection UI.
Additional delays at the start of the process
After tapping "Start", the Asda machine shows a "This checkout will only accept credit and debit cards" modal for several seconds before the checkout process can start.
Who makes self-checkouts machines?
Input latency is impacted by software and hardware factors. A more powerful checkout machine will run even unoptimized code more quickly. So who produces self-checkout machines?
All except one of the checkout machines I used were made by the same two manufacturers: NCR Voyix and Diebold Nixdorf.
| Manufacturer | Shop |
|---|---|
| NCR Voyix | Sainsbury's, Asda, Boots, TGJones |
| Diebold Nixdorf | Tesco, Aldi, Marks & Spencer |
| DataLogic | Lidl |
This may vary by store location. Different models from the same manufacturer will also have different performance characteristics.
Conclusion
If input latency is your primary concern, Aldi is the best place to shop. Not only do the buttons there respond the fastest, but they also don't bother asking if you want bags or showing you membership reminders.