# Device detection issues
Fastly's Server-side device detection is based on User Agent (opens new window) and can't recognize all the devices. At Marfeel, this means that in some cases, it is possible to see the desktop version when mobile is expected.
# Solution
Ask the tenant to add the Garda.js script to the beginning of all their pages.
When server-side device detection fails, if Garda.js is present it executes and detects the right device. For all other cases, there is no impact: Marfeel activation still only depends on the CDN.