Check For Datatype

I need to write a trigger to check to see if a field's value is the correct datatype before saving it to the database. Here is what I have so far:

CREATE TRIGGER [CheckMinutesFormat] ON [dbo].[DowntimeDetail]
FOR INSERT, UPDATE
AS
if (select downtimeminutes from inserted) <> datatype(bigint)
begin
raiserror('Downtime minutes must be a numeric value.', 16,1)
rollback transaction
end

I KNOW this is not correct (the part in red). I don't know the syntax to check for a bigint datatype...please help.

Thanks!
Jamie