If you are using the OOTB FAST Search Center site template then by default you get a tab for People search on the main page. On this tab you get a Search Options link, which  brings up the dropdown box that allows you to search by certain properties of the user profile:

How do you add a custom property to this dropdown? For example, you allow users to indicate if they are a First Aid Officer in their profile. You want users to be able to search for First Aid Officers in the organisation.

To achieve this you must first define the custom property for your user profile and map it to a managed property. I will not cover this as this post is more about configuring the Search Options dropdown. Just be sure to tick the Indexed option in the Search Settings section when defining the new property.

You can control the fields being shown in the Search Options dropdown by setting the Properties property of the People Search Box (which is a web part). This property holds a piece of XML and can be edited right in the SharePoint UI by editing the web part. (This property can be found under the Miscellaneous category in the web part editor.)

OOTB, this XML is as below:

<Properties>
	<Property Name="LastName" ManagedName="LastName" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:LastName"/>
	<Property Name="FirstName" ManagedName="FirstName" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:FirstName"/>
	<Property Name="JobTitle" ManagedName="JobTitle" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-JobTitle"/>
	<Property Name="PersonKeywords" ManagedName="PersonKeywords" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-PersonKeywords">
		<EffectiveProperty Name="Responsibility" ManagedName="Responsibility" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Responsibility"/>
		<EffectiveProperty Name="Skills" ManagedName="Skills" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Skills"/>
		<EffectiveProperty Name="Interests" ManagedName="Interests" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Interests"/>
	</Property>
</Properties>

As you can see the four Property elements in the XML map to the four options you see on the dropdown. The attributes of each Property element is pretty self-explanatory:

• Name: appears to be the display name that will appear on the dropdown
• ManagedName: the name of the managed property that will be searched
• ProfileURI: this is the name of the crawled property. You can get this by viewing the crawled property in Central Admin as shown below:

So, to add my First Aid Officer field, I would use this XML:

<Properties>
	<Property Name="LastName" ManagedName="LastName" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:LastName"/>
	<Property Name="FirstName" ManagedName="FirstName" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:FirstName"/>
	<Property Name="JobTitle" ManagedName="JobTitle" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-JobTitle"/>
	<Property Name="Is First Aid Officer" ManagedName="IsFirstAidOfficer" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:IsExecutiveAssistant"/>
	<Property Name="PersonKeywords" ManagedName="PersonKeywords" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-PersonKeywords">
		<EffectiveProperty Name="Responsibility" ManagedName="Responsibility" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Responsibility"/>
		<EffectiveProperty Name="Skills" ManagedName="Skills" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Skills"/>
		<EffectiveProperty Name="Interests" ManagedName="Interests" ProfileURI="urn:schemas-microsoft-com:sharepoint:portal:profile:SPS-Interests"/>
	</Property>
</Properties>

And here is the result:

The last thing to note is if your property is a boolean (yes/no), then you will have to use 1 or true as the search value.