In 1841, well-known convict architect James Blackburn designed the two sandstone watch houses at the entrance to St John's Avenue. Both had an entrance porch. Blackburn's original plan for No.1 had two main rooms, one for men and one for women, and three smaller rooms (cells?). No.2 had three main rooms for constables.
Blackburn's watch houses may not have been the first on the site. Charles Bruce's etching in 1831 depicts two watchhouses in a similar location but there is no evidence that they were built. In the early 1840s, it was reported that
“A Watch house is very much required at New Town on the main road - where the population is thick - and I should feel obliged by His Excellency The Governor authorizing a sum not exceeding 200 pounds to be paid for this service and arrangements with the Director General of Public Works be made to put up the building - The Head Master of the Queen's Orphan School is very anxious to have a Watch house and residence as lodges at the entrance to the Orphan School property heading to the Church.”
The watch houses have had a variety of uses and are also known as gate houses. At one stage, No.1 St John's Avenue was used for the Hobart District Nursing Service and now hosts the Mental Health Carers of Tasmania. No.2 now houses the offices of Hobart Hackerspace Inc.
The watch houses are an essential part of the St Johns precinct, these buildings although not to the original John Lee Archer design, are fine examples of Blackburn's ability. The relationship of the buildings to St Johns Church is very powerful and reinforced by the avenue planting. An example of bold and imaginative planning in colonial times.