- type <varname>Wants</varname> from
- this unit to all listed units. This
- may be used to activate aritrary units
- if a specific device becomes
- available.</para></listitem>
+ type <varname>Wants</varname> from the
+ device unit to all listed units. The
+ first form is used by the system
+ systemd instance, the second by user
+ systemd instances. Those settings may
+ be used to activate arbitrary units
+ when a specific device becomes
+ available.</para>
+
+ <para>Note that this and the
+ other tags are not taken into account
+ unless the device is tagged with the
+ <literal>systemd</literal> string in
+ the udev database, because otherwise
+ the device is not exposed as a systemd
+ unit (see above).</para>
+
+ <para>Note that systemd will only act
+ on <varname>Wants</varname>
+ dependencies when a device first
+ becomes active. It will not act on
+ them if they are added to devices that
+ are already active. Use
+ <varname>SYSTEMD_READY=</varname> (see
+ below) to influence on which udev
+ event to trigger the dependencies.
+ </para></listitem>