Sql Server Case. . When. . in Statement

Thanks for the Answer I have modified the statements to look like below

SELECT
     AlarmEventTransactionTable.TxnID,
     CASE 
    WHEN DeviceID IN('7', '10', '62', '58', '60',
            '46', '48', '50', '137', '139',
             '141', '145', '164') THEN '01'
    WHEN DeviceID IN('8', '9', '63', '59', '61',
            '47', '49', '51', '138', '140',
            '142', '146', '165') THEN '02'
             ELSE 'NA' END AS clocking,
     AlarmEventTransactionTable.DateTimeOfTxn
FROM
     multiMAXTxn.dbo.AlarmEventTransactionTable

Try this...

SELECT
    AlarmEventTransactionTableTable.TxnID,
    CASE
        WHEN DeviceID IN('7', '10', '62', '58', '60',
                 '46', '48', '50', '137', '139',
                 '142', '143', '164') THEN '01'
        WHEN DeviceID IN('8', '9', '63', '59', '61',
                 '47', '49', '51', '138', '140',
                 '141', '144', '165') THEN '02'
        ELSE 'NA' END AS clocking,
    AlarmEventTransactionTable.DateTimeOfTxn
 FROM
    multiMAXTxn.dbo.AlarmEventTransactionTable

Just remove highlighted string

SELECT AlarmEventTransactionTableTable.TxnID, CASE AlarmEventTransactions.DeviceID WHEN DeviceID IN('7', '10', '62', '58', '60', ...)

It might be easier to read when written out in longhand using the 'simple case' e.g.

CASE DeviceID 
   WHEN '7  ' THEN '01'
   WHEN '10 ' THEN '01'
   WHEN '62 ' THEN '01'
   WHEN '58 ' THEN '01'
   WHEN '60 ' THEN '01'
   WHEN '46 ' THEN '01'
   WHEN '48 ' THEN '01'
   WHEN '50 ' THEN '01'
   WHEN '137' THEN '01'
   WHEN '139' THEN '01'
   WHEN '142' THEN '01'
   WHEN '143' THEN '01'
   WHEN '164' THEN '01'
   WHEN '8  ' THEN '02'
   WHEN '9  ' THEN '02'
   WHEN '63 ' THEN '02'
   WHEN '59 ' THEN '02'
   WHEN '61 ' THEN '02'
   WHEN '47 ' THEN '02'
   WHEN '49 ' THEN '02'
   WHEN '51 ' THEN '02'
   WHEN '138' THEN '02'
   WHEN '140' THEN '02'
   WHEN '141' THEN '02'
   WHEN '144' THEN '02'
   WHEN '165' THEN '02'
   ELSE 'NA' 
END AS clocking

...which kind makes me thing that perhaps you could benefit from a lookup table to which you can JOIN to eliminate the CASE expression entirely.