diff --git a/bin/omarchy-hw-fingerprint b/bin/omarchy-hw-fingerprint
index 03af4fdb..6f4b407b 100755
--- a/bin/omarchy-hw-fingerprint
+++ b/bin/omarchy-hw-fingerprint
@@ -9,6 +9,7 @@
 # also make USB touchscreens) are left out to avoid nagging laptops with no
 # reader — those still match on the product string below when present.
 fingerprint_vendors=" 27c6 138a 06cb 08ff 1c7a 147e "
+usb_devices_path="${OMARCHY_USB_DEVICES_PATH:-/sys/bus/usb/devices}"
 
 # libfprint drives every reader it supports from userspace over libusb, so a
 # real reader sits there with no kernel driver bound to any of its interfaces.
@@ -24,16 +25,19 @@ has_kernel_driver() {
   return 1
 }
 
-for dev in /sys/bus/usb/devices/*; do
+for dev in "$usb_devices_path"/*; do
   # The device's own product descriptor usually names it, e.g. "Goodix
   # Fingerprint USB Device" — driver-independent and vendor-agnostic.
   if [[ -r $dev/product ]]; then
     product=$(<"$dev/product")
     product=${product,,}
-    # Elan's match-on-chip readers report "ELAN:ARM-M4", the family name
-    # rather than the function. Elan is left out of the vendor list above
-    # on purpose, so without this they match nothing.
-    [[ $product == *fingerprint* || $product == *biometric* || $product == *elan:arm-m4* ]] && exit 0
+    # Elan's match-on-chip readers report "ELAN:ARM-M4" and Fingerprint Cards'
+    # report "FPC Sensor Controller" or "FPC L:0000 FW:1425046" — the family or
+    # the manufacturer rather than the function. Both vendors are left out of
+    # the list above on purpose (Elan also makes touchscreens), so without these
+    # they match nothing. FPC leads the string on every reader on record, and
+    # three letters are little to match on, so require the prefix.
+    [[ $product == *fingerprint* || $product == *biometric* || $product == *elan:arm-m4* || $product == "fpc "* ]] && exit 0
   fi
 
   if [[ -r $dev/idVendor ]]; then
diff --git a/test/shell.d/hw-fingerprint-test.sh b/test/shell.d/hw-fingerprint-test.sh
new file mode 100755
index 00000000..78525c86
--- /dev/null
+++ b/test/shell.d/hw-fingerprint-test.sh
@@ -0,0 +1,91 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+tmp_dir=$(mktemp -d)
+trap 'rm -rf "$tmp_dir"' EXIT
+
+write_usb_devices() {
+  rm -rf "$tmp_dir/devices"
+  mkdir -p "$tmp_dir/devices"
+
+  local index=0
+  local spec
+  for spec in "$@"; do
+    local vendor=${spec%%:*}
+    local remainder=${spec#*:}
+    local product_id=${remainder%%:*}
+    # A spec with no third field describes a device with no product
+    # descriptor. Without this guard ${remainder#*:} would return the product
+    # id unchanged and quietly write it out as the product string.
+    local product=""
+    if [[ $remainder == *:* ]]; then
+      product=${remainder#*:}
+    fi
+    local dev="$tmp_dir/devices/1-$index"
+
+    mkdir -p "$dev"
+    printf '%s\n' "$vendor" >"$dev/idVendor"
+    printf '%s\n' "$product_id" >"$dev/idProduct"
+    [[ -n $product ]] && printf '%s\n' "$product" >"$dev/product"
+    index=$((index + 1))
+  done
+}
+
+hw_fingerprint() {
+  OMARCHY_USB_DEVICES_PATH="$tmp_dir/devices" "$ROOT/bin/omarchy-hw-fingerprint"
+}
+
+assert_detects() {
+  local description="$1"
+
+  hw_fingerprint || fail "$description"
+  pass "$description"
+}
+
+assert_rejects() {
+  local description="$1"
+
+  if hw_fingerprint; then
+    fail "$description"
+  fi
+  pass "$description"
+}
+
+write_usb_devices '10a5:a305:FPC L:0000 FW:1425046'
+assert_detects "an FPC reader is detected by its product string"
+
+write_usb_devices '10a5:1234:Generic USB Device'
+assert_rejects "a generic 10a5 USB device is not detected"
+
+write_usb_devices '10a5:9800:FPC Sensor Controller L:0002 FW:25.26.23.14'
+assert_detects "an FPC reader is detected by its sensor-controller string"
+
+# Pins the match to a prefix. FPC abbreviates unrelated things too, and this
+# branch is trusted with no kernel-driver check, so the token is not enough.
+write_usb_devices '0bda:5842:USB2.0 FPC Camera'
+assert_rejects "an FPC token mid-string is not detected"
+
+write_usb_devices '1234:5678:Goodix Fingerprint USB Device'
+assert_detects "a reader is detected by an existing product-name match"
+
+write_usb_devices '27c6:1234'
+assert_detects "a reader is detected by an existing vendor match"
+
+bind_driver() {
+  local dev="$1" driver="$2"
+
+  # sysfs links the interface at a driver directory, and the detector's [[ -e ]]
+  # follows the link, so the target has to exist for this to model anything.
+  mkdir -p "$tmp_dir/drivers/$driver" "$tmp_dir/devices/$dev"
+  ln -sf "$tmp_dir/drivers/$driver" "$tmp_dir/devices/$dev/driver"
+}
+
+write_usb_devices '27c6:1234'
+bind_driver '1-0/1-0:1.0' uvcvideo
+assert_rejects "a vendor guess bound to a kernel driver is rejected"
+
+write_usb_devices '1234:5678:Generic USB Device'
+assert_rejects "a machine with no matching USB devices detects nothing"